EDIT: See the great answers by u/Klesk_vs_Xaero to this question: good context and expands to cover Italy’s actions in Europe.

During the Italian invasion of Ethiopia in 1935, a number of war crimes were committed. The Italians bombed hospitals and ambulances, deployed mustard gas via airplane and artillery shell, mutilated prisoners, and used expanding bullets. After the fall of Addis Ababa, the Italians resorted to similarly brutal methods to tamp down resistance. The worst example occurred after Ethiopian partisans attempted to assassinate the Italian viceroy in Ethiopia, Marshal Rodolfo Graziani on February 12, 1937 by throwing grenades at him during a public ceremony.

Italian forces responded by firing into the crowd. For the remainder of the weekend, Italian soldiers killed Ethiopians indiscriminately; they chased and stabbed people in the streets, set fire to houses, and broke into the homes of foreign nationals to drag out and hang Ethiopians they were trying to protect. Hundreds took refuge in the American consulate, but went home after the Americans received guarantees about their safety from Italian officials. After the Ethiopians left, they were rounded up by Italians, taken a short distance away, and killed en masse.

The Italians arrested a small group of young intellectuals Ethiopia's Emperor Haile Selassie had sent overseas to acquire college degrees. Torture was liberally used in their interrogations, including one method where a victim was wrapped from neck to toe in rope and then soaked in water. The swelling ropes would tighten until blood was oozing out of the victim's pores. Their execution by firing squad was almost a mercy.

Thousands of Ethiopians were sent to concentration camps, one near Mogadishu and one on an arid island in the Red Sea. Relatives who tried to bring food or find their loved ones were flogged and sometimes thrown into the camps as well. The rations were kept at starvation levels, and the prisoners were worked mercilessly on sugar cane and banana plantations personally owned by Italian officials. Dysentery and malaria were rampant, and prisoners were picked out for execution on a daily basis. As many as half of the internees died before the camps were closed and the survivors were released.

The massacre and its aftermath, known in Ethiopia as Yekatit 12 (after the date in Ethiopia's calendar), killed perhaps 20,000 people, a quarter of Addis Ababa's population. Overall, the Italian invasion killed at least a quarter-million Ethiopians, and many thousands more died during their occupation before British forces and Ethiopian partisans ended Italian rule in 1941. Throughout the occupation, despite a shift to a more conciliatory tone and Italian efforts to showcase infrastructural development and enlightened modernization, the Italians enacted harsh racial laws that set up an apartheid-like separation between the Ethiopians and Italian colonizers. Italian women who were convicted of sex with Ethiopian men faced concentration camp sentences. Ethiopians who resisted Italian authority could expect torture and detention on the for-profit labor camps set up by corrupt Italian officials.

Sources:

The Addis Ababa Massacre: Italy's National Shame, by Ian Campbell

Fascist Modernities: Italy, 1922-1945, by Ruth Ben-Ghiat

I am afraid of that “on par” - I understand what you mean and I am not blaming you for a general trend; but I'll try to explain why I have a problem with it and why I think there is little to be gained in ranking historical atrocities.

I also have to state upfront that my knowledge of fascism is more oriented towards the social-political matters; fascist war crimes are not exactly my main area of expertise (and probably literature on the matter is also not as abundant as that on other fascist things – especially for the Yugoslav occupation).

That said, if I were to answer your question to the letter, I'd tentatively go with “no”. The Italian Fascist Regime (I want to stress the amount of weight I am putting on those commas!) did not perform “that specific sort of large scale atrocities” during the war, or before. A pitiful distinction if one wants to use it as an exculpatory argument; since it certainly committed actions that qualified as war crimes, violating the current regulations as well as – obviously – going against the more stringent interpretation that arose after the war. But it also displayed a general inclination to expand such approach, and make it more systematic – especially in the context of its “African Empire”- so that one might really question whether the scale limitations were just a consequence of inadequate time and material means. And since it is beyond question that those actions were reprehensible to a degree that even the delusions of racial superiority could barely hide.

The history of Italian “atrocities” is very closely tied with that of Italian colonialism. Unfortunately a general treatment of the matter has been postponed by Italian historiography for quite a long time – the exception being the contributions of Giorgio Rochat and the more popular works of Angelo Del Boca.

The first notable example of systematic violations of “the people's right” took place during the so called “pacification of Libya” during 1922-32. Italy had been forced to abandon most of the occupied lands of Tripolitania during the First World War, due to a combination of local guerrilla and allocation of men and resources to the more urgent Austrian front. In 1922 the Italian authorities (under the imprint of the Governor Giuseppe Volpi) begun a policy of reclamation of the land – that is the cultivable land, close to oasis or coastal inhabited regions – from the locals; they declared their right to seize any land not permanently irrigated for which the “Arabs” [sic.] did not possess a written deed. For those who had such deed, it was still possible to proceed to alienate their lands, with financial compensations established by the authorities well below the market value of the land. The intention was – explicitly so – to take the land from the locals and make it available for the Italian colonists.

The result of the government decrees was that the Italian authorities were able to seize over 64,000 hectares of land (to 1926 and rising to 200,000 by 1930) without one instance of legal opposition arising. This was in fact the purpose – as the publication of state functionary Filippo Cavazza (which is full of interesting legal considerations) explains: “it is true that such a system doesn't possess the merits of a substantial legal basis, it does not fit into a well defined juridical framework, and does not approach directly any legal matter. […] But it has the merit of avoiding them all. And above all it gives the most convenient result from a political and juridical point of view”.

Contextually with this new policy of reclamation of the land, more energetic measures of control of the population were enacted. While the locals living in the coastal regions had more or less complied with the Italian new regulations, the people of the interior regions could not really surrender their customary uses of the common lands for pasture and cultivation. Through 1928-1932 General Rodolfo Graziani was tasked with the matter of suppressing the local resistance (something Graziani would build a reputation for). The first stage of the repression had taken place closer to the coast of Tripolitania, the second one moved into the internal Gebel region. There Graziani expanded the methods previously employed: deportations of the people towards the concentration camps set up on the coast (in the words of Graziani himself, “On June 25^th the removal of the entire population of Gebel was decided”), systematic seizing of land, killing of livestock, rapid strikes supported by aviation and mechanized troops. From 1926 to 1933 we are looking on a reduction of roughly 85% in the livestock numbers - for a population which relied heavily on those animals for sustenance, the results were obvious. Unfortunately the numbers of civilian deaths are less easy to establish but historian G. Rochat estimated some 60,000 dead over 225,000 inhabitants.

The “pacification” was notoriously brought to completion with the “notable” execution of the rebel leader Omar al Muktar. And Graziani could observe in his memorial on the “pacification” that “nothing new can be built, unless one destroys […] a past that is no longer adapting to the present”.

The adventures of Italian colonialism continued with the more well known episode of the Ethiopian Conquest of 1935-36. There Fascism resumed the plans for an expansion that had been shelved at the end of the XIX Century, expansion starting from the poor coastal land known at the time as Italian Somalia. The first plans for a hostile military action against Ethiopia were drafted in 1932 but the idea of an invasion grew into a more concrete plan during 1934 (Mussolini approved the preparations on December 30^th arguing that the international situation allowed a good opportunity to act without significant repercussions: “it was necessary to solve the issue as soon as possible” with the immediate purpose being “the destruction of the Abyssinian armed forces and the total conquest of Ethiopia”), and so grew the amounts of men and resources destined to the endeavor: 111,000 men (plus 53,000 askari), 35,500 horses and mules, 4,200 machine guns,126 planes at the beginning – 330,000 men (plus 87,000 askari), 90,000 quadrupeds, 10,000 machine guns at the end of the conflict.

The large amount of means made available by the government – that was looking for a swift and impressive military victory, rather than an old school colonial war, and made very little effort to limit military expenditure – and the difficult situation of the Ethiopians in so far as supplies and transportation were concerned, created the precondition for an easy military victory.

The “no means spared” approach taken by the Italian military and political leadership included those means that constituted a clear violation of international right – that is the substantial and repeated use of asphyxiating gas (both during the conflict and later on during the successive repression – and repeatedly approved by Mussolini himself as various telegrams to Generals Badoglio and Graziani show). It is extremely hard to establish what fraction of the local dead can be ascribed to the use of poison gas and what to conventional war methods. It is evident though that the explicit choice to use such an instrument – especially in a situation where the use was by no means a necessity – betrayed the attitude of the fascist leadership towards the Ethiopian population as a whole; the idea of sparing civilian casualties appears to have been entirely foreign to their minds.

Nor can the use of summary executions as a way to keep order in the newly conquered regions be ascribed to spontaneous excesses – rather it had been preemptively approved by Mussolini, for instance on May 3^d 1936 instructing Badoglio that “once occupied Addis Abeba […] anyone found within the city or its surroundings with armed hands was to be summarily executed […] all those known as young Ethiopians [local resistance] to be summarily executed […] all those who had taken part to violence or plunder be summarily executed […] those who, within 24 hours, had not surrendered their weapons be summarily executed”. And then again on July 8^th Mussolini “authorized [Graziani] to initiate and enact a systematic policy of terror and extermination against the rebels and the complicit population”. As late as September 1937 Graziani was again authorized to make use of asphyxiating gas against the rebels.

The aftermath of the Italian conquest was marked by a systematic and deliberate exauthoration of the local ruling class in observation of a manner of “segregation” that was contemporaneously sanctioned by the development of the racial legislation (1938). The result was a plan of social regulation that clearly divided the locals from the Italians in terms of civil and public rights, that extended to cultural prohibitions, as of language, religion and customs. Notable was the persecution of the Copts in the region – with their convents often accused of harboring rebels in the aftermath of the attempted murder of Graziani (on February 19^th 1937) – as well as the prohibition of the traditional religious forms.

But none of these measures succeeded in pacifying the region – despite a larger scale application of the same methods of deportation and killing of livestock employed in Libya – and Ethiopia was still in revolt when Italy begun its unfortunate WW2 adventure and the African lands were eventually reclaimed from their usurpers.

As for the numbers, those given by the Ethiopian governments account for over 300,000 war casualties and over 100,000 killed in the following repressions. Another 300,000 were estimated dead in consequence of the killing of their livestock.

What was the Vatican's stance to fascist Italy? Just seems really at odds.

Where did all of the Italian Jews go?

Its often overlooked as Italy just before the start of the second world war shared with Nazi Germany the first civilian bombardments.

We bombarded Guernica with the Nazis during the Spain Civil war(1936-1938) and many other cities, for the first time aiming at civilians. Actually most of the Nazifascist support for Franco was a way to experiment new ways of war.

But the most cruel exploit of Italy happened after Germany annexed Austria: Mussolini, to send a message, ordered to start a new method of bombardment of Barcellona "Iniziare da stanotte azione violenta su Barcellona con martellamento diluito nel tempo" a constant and long bombardment of the city.

Between 16 march and 18 march 1938 Barcellona was bombarded for 2 consecutive days, a new wave of bombs was sent every 3 hours for a total of 44 tons of bombs aiming not at just killing but mainly terrorizing the population.

This strategic bombardment was going to be the main bombardment tactic in the second world war.

Not surprisingly it was italians that invented air bombardments in 1911, but only after the spanish Civil war that strategy was going to really be perfected.

Edit: added a few dates.