He warned that the Russians and Iranians would be making a grave humanitarian mistake to cause hundreds of thousands of people to be killed. The statement came as the Assad regime prepares phased offensive to regain Idlib.
Idlib province and surrounding areas are the last major enclave held by insurgents fighting President Bashar al-Assad. Some 3 million civilians live there. The UN and humanitarian aid organizations say an attack on Idlib could be the worst catastrophe in the 7-year civil war.
On Monday, Iranian Foreign Minister Mohammad Javad Zarif led a diplomatic delegation to Damascus to meet with President Assad and prepare for the Russia-Iran-Turkey summit in Tehran on Friday.