Israel is locked in now, no amount of diplomacy will stop them, not even the US. Israel won't trust China and Russia's word on this, they will want it fool proof by blowing it up themselves.
Besides I don't even think it is because of nuclear weapons they're doing this, nuclear weapons is just an excuse. They dare to do this precisely because they know Iran don't have nuclear weapons and is not even close to assembly. Otherwise they will just be forcing Iran's hand to accelerate nuclear works, which is foolish.
They want to destroy Iran, simple as that