Russian air raids ceased in and around Idlib on August 15, but pro-regime forces have maintained an aerial bombardment and shelling there, the war monitor said. "Syria's territorial integrity should be safeguarded and all tribes and groups, as one society, should start the reconstruction process, and the refugees should return to their homes", he said.
Iranian President Hassan Rouhani will host his Turkish and Russian counterparts Recep Tayyip Erdogan and Vladimir Putin, respectively, on September 7 in an attempt to find ways to end the ongoing crisis in Syria.
His forces are amassing around the province of Idlib, presumably in preparation for the assault.
He added: "Hundreds of thousands of people could be killed".
"They shared identical views on the importance of strengthening bilateral coordination and political discussions in the coming phase", a statement said.
Turkey, which has long supported anti-Assad rebels, has cooperated with Russian Federation and Iran on talks over Syria in recent years and has troops in the Idlib region on an observation mission.
An estimated three million people - half of them displaced from other parts of Syria - live in the province and adjacent rebel-held areas.
The SOHR said the air strikes were in the countryside near Jisr Al Shughour on the western edge of the rebels' northwestern territory.
Iran has been also helping Damascus in its fight against various factions of terrorists on its soil through providing the government troops with advisory assistance, based on an invitation by the Syrian government, since foreign-backed militancy broke out in the Arab country in March 2011.
ICG said Russian Federation, whose air support would be crucial for the offensive to succeed, should understand that a bloodbath in Idlib would jeopardise its own political goals.
"Russia seeks to ensure not just the regime's military victory in Syria but its full political restoration through worldwide re-legitimation at war's end".
But Israeli Defense Minister Avigdor Lieberman on Monday signalled strikes could be extended to Iraq if necessary.
Britain, France and the United States, which together launched limited attacks on Syrian installations in mid-April in retaliation for an alleged Syrian chemical attack, say their red line against illegal weapon use remains in force.
"Frankly speaking, I don't think there's anything the United States can do about it".