I'm not proud of this, but during WW2 my government bombed beseiged and starving Japanese garrisons with Bully Beef tins that had been slightly opened and left to "ripen" a few days beside a jungle airstrip.

That was illegal, but fully deniable. Also not very effective.

This is only the next step down the war crimes ladder. Okay, the use in civilian areas makes it two steps down.