There might be some potential legal defense in terms of proportionality of collateral damage but it's so thin here as to be absurd.
Regardless, given the number of war crimes this army has been found guilty of, this is somewhat moot. What's another war crime in the grand scheme of things.
There's no central enforcement of international war crime law, so this thread on legal technicalities isn't particularly relevant in real terms, but there is at least an arrest warrant out for the (former) Minister for Defence & Prime Minister in 124 countries, so there's not a lot of room for ambiguity here.
Regardless, given the number of war crimes this army has been found guilty of, this is somewhat moot. What's another war crime in the grand scheme of things.