Families in Idlib have begun fleeing from frontline villages and fashioning homemade gas masks  in anticipation of an assault by Assad regime forces as early as this weekend. 

The 2.5 million civilians trapped in Syria’s last rebel-held province are bracing for an attack to begin after a major summit between Iran, Russia and Turkey on Friday.  

Around 1,000 people fled from villages in southeast Idlib, close to where an attack by regime troops is likely to begin, according to the Syrian Observatory for Human Rights. 

Other began making gas masks out of plastic cups filled with cotton and charcoal in case Assad’s forces use chemical weapons during the attack. 

"We are preparing what little we can: small primitive masks we can place on our children’s mouths in case we are hit with chemicals," one father told Reuters from his village near Idlib city.

Both the US and France have warned that they are prepared to again launch strikes against the Assad regime if it uses chemical weapons in Idlib.

"We are ready to strike if chemical weapons were used again," said General Francois Lecointre, the head of the French military. 

But while Western powers have warned against the use of chemical weapons, there is little appetite for intervention to stop a conventional assault.  

Donald Trump, the US president, warned that if there was “a slaughter” in Idlib then “the world is going to get very, very, very angry, and the US is going to get very angry”. He declined to say the US would step in to prevent an attack. 

The fate of Idlib is likely to be decided at a three-way summit in Tehran on Friday between Vladimir Putin, the president of Russia, Hassan Rouhani, the president of Iran, and Recep Tayyip Erdogan, the president of Turkey. 

The UN has said it expects the assault would only begin after the talks.

All three countries have expressed an interest in some sort of deal, under which rebel and jihadist forces would surrender to avoid major bloodshed. 

Ali Larijani, the speaker of Iran’s parliament, said he “really hoped” a deal could be reached at the summit. 

Russia continued to take a hard line, saying it was duty bound to wipe out terrorist groups in Idlib.

Russia is particularly concerned about militants using the province as a staging ground for attacks against its airbase in the coastal city of Latakia.  

“We have killed, we are killing and we will kill terrorists,” said a spokeswoman for Russia’s foreign ministry. 

Jan Egeland, a UN advisor on Syria, acknowledged that there were terrorist groups in Idlib but said that did not justify an all-out attack on an area crowded with civilians. “There are more babies than terrorists,” he said.