Yes, Guatemala has historically claimed that Belize should be part of its country and it still remains a large issue in the country. The country claims that they inherited the Spanish claims on Belize, from the Sibun River south.

This can go back to the Anglo-Guatemalan Treaty of 1859, where Guatemala would recognized Belize as part of the British Crown, and in return, the British Crown would ensure Guatemala has adequate communication to the Atlantic by road or rail. Starting around the 1930's and 1940's, Guatemala started saying that they never received the adequate access that was promised to them and therefore the treaty is null (Which the ICJ ruled that Guatemala still has to respect the border with Belize).

The US tried to mediate talks in the 60's between the countries to resolve the issue, and around this time, the countries in the Central American region, who formally supported Guatemala, started to begin switching support to Belize.

The Heads of Agreement was a 1981 attempt to mediate the issue between the United Kingdom, Belize, and Guatemala. The Belizean people felt that the agreed upon conditions were giving too much to Guatemala that issued a proclamation of independence later that year, and was granted it, with the dispute ongoing.

Guatemala refused to recognize Belizean independence until 1991, although talks of negations occurred between the two countries started in 1988.

Even to this day, it remains a very controversial issue. The current President of Guatemala, Jimmy Morales, who was inaugurated only a couple of weeks ago, has gone on record saying that "The most deplorable event – among all the things that have happened in Guatemala, there are certain things that are not spoken about and which I believe we should. Everything that goes contrary to national unity and territorial integrity are things that should hurt us. Something is happening right now, we are about to lose Belize. We have not lost it yet."