Now I do seem to recall us bombing a caravan with Russian advisors that were most likely carrying weapons (or at least wanted members of Saddam's administration) towards the Syrian border.
I can certainly see how that becoming a much bigger controversy would not have been helpful.
Did you know that at the outset of our arming afghanistan against Russia in the 80's we armed them with russian arms only through Pakistan so it would not be traced backed to the US. Later on we let them have US made stingers but from the begining it was all covert.
Sorry but I don't buy that explanation. All the world knew that Iraq's weapons came from the USSR and France. That would have not been surprise nor would it have required any confrontation since these were deals going back decades between sovereign states most of which predated even the first Iraq war.