By modern lights, yes. Churchill's sanction of the Hamburg Fire Attack and Truman's decision to nuke a second Japanese city alone would count as war crimes by current definitions as both leaders were certain of massive civilian casualties and made no efforts to minimize or limit those deaths. In fact, it can be argued that both leaders sought those civilian deaths in acts of terrorism (modern definition) designed to break the will of the opposition. In Truman's case, it can be argued that the act of terror worked.
Remember, however, that if you apply modern definitions to the acts of the past, most human cultures are little except for a collection of war criminals and thugs. Most of the Roman justice code involved what is labeled torture by modern definitions. The Feudal system of Western Europe was based on serfdom (functionally on slavery). Drogheda & Badajoz were sacked because they did not surrender when outnumbered and had to be assaulted. Aussie infantry in the trenchs of the Western Front were noted for their "too late chum" practice of bayonetting any surrendered German who -- in their opinion -- had been firing their weapon for too long before surrendering.
Be careful when applying modern definitions of morality and ethics to the past. Such applications are not without value, but they rarely account for the "there-then" context of those actions very well.
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