By Tom Perry, John Irish and Bozorgmehr Sharafedin BEIRUT/PARIS/DUBAI (Reuters) - France and Iran voiced concern over escalating violence in Syria on Tuesday, echoing warnings from the United States and Russia as fighting near the city of Aleppo put more pressure on a fragile truce agreement. The already widely violated "cessation of hostilities" agreement brokered by Russia and the United States has been strained to breaking point by an upsurge in fighting between Syrian government forces and rebels near Aleppo.