In northwestern Syria, 68-year-old Abu Khaled was among dozens to have set up camp in a field, hoping that Turkish soldiers nearby would shield him from bombardment by Bashar al-Assad's regime.

Hundreds of civilians have fled villages near the front line in Syria's Idlib province fearing an imminent regime assault on the country's last major rebel bastion, a monitor said Thursday.

Russia-backed government forces have been massing around the northwestern province for weeks, while on Tuesday Moscow carried out its first air strikes on the rebels in three weeks.

US President Donald Trump on Monday warned Syria against launching an attack on the country's last rebel stronghold with the help of Russia and Iran, saying the offensive could trigger a "human tragedy."

An air strike near a US base in southeastern Syria has killed at least eight pro-government fighters, the Syrian Observatory for Human Rights reported Monday.

Four Syrians, one Iranian national and three other non-Syrian fighters were among the casualties of the strike carried out on Saturday, the war monitor said.

Iran's foreign minister held talks with officials in Syria on Monday as Syrian forces and their allies prepare for an assault on the last opposition stronghold in the country.

Syria's foreign ministry and Iran's state-run IRNA news agency said Mohammad Javad Zarif was received by Deputy Foreign Minister Faisal Mekdad upon his arrival in Damascus, and was to meet later with Syrian President Bashar Assad.

Israel on Wednesday renewed its threat to attack Iranian military targets in Syria, after Tehran and Damascus signed an accord on security cooperation.

At least 27 people are being held by the Islamic State group in southern Syria, Human Rights Watch said Saturday as it deplored the hostage-taking as a "war crime".

Turkish Foreign Minister Mevlut Cavusoglu warned Friday that seeking a military solution in Syria's last rebel-held province of Idlib would lead to disaster.

The UN peace envoy for Syria will host Iran, Russia and Turkey for talks on drafting a new Syrian constitution on September 11-12, a United Nations spokeswoman said Friday. 

The leader of Syria's al-Qaida affiliate has vowed to fight on in Idlib province, the country's last major rebel stronghold, in the face of a possible government offensive.

Abu Mohammed al-Golani of the militant Levant Liberation Committee says state-sponsored surrenders of rebel groups, similar to those that recently occurred in southern Syria, won't happen in Idlib.