If it were done using a hellfire missile from a drone would that be called an illegal "assassination"? The idea that assassinations are more illegal or immoral than -- say -- firing hellfire missiles at suspicious looking people in countries we don't care for is pretty silly.

That said, I'm sure that if the US was involved there was some kind of backwards hoop jumping so as not to technically break the law. "I just had a chat with him on a park bench when we bumped into each other. He said he'd look into it."