Yes. The Rape of Nanking was widely reported, as was poor Japanese treatment of Allied POWs (e.g. the Bataan Death March). Indeed, the question of whether the Emperor himself would be tried for war crimes was a sticking point of Japanese attempts to reach a diplomatic end of the war and played a role in the Potsdam Conference.

But if you're asking, "did people think this justified using the atomic bombs?", that's a separate and trickier question. (Some people thought the "barbarity" of the Japanese justified barbarity back, some people thought two wrongs don't make a right.)