Aid agencies on Friday (October 12th) warned of dire humanitarian consequences if a deal to avert a regime assault on Syria's last major opposition stronghold was not fully implemented within days, AFP reported.

Russia and Turkey agreed last month to set up a buffer zone around Idlib province to separate opposition fighters and extremist groups inside from Syrian regime and allied fighters massing on its edges.

Under the accord, extremist groups have until Monday to withdraw from the buffer zone semi-circling the region of some three million people, but have not yet shown any sign of moving.

On Friday, international aid groups working in Idlib warned that failure to implement the deal could spark renewed violence and trigger mass displacement.

Local partner organisations and civilians receiving aid "have expressed fears that violence could spiral out of control in the next few days if either the deal collapses or fighting escalates in areas not covered by it", they said.

"Even a limited military offensive would displace hundreds of thousands of people," CARE International, the International Rescue Committee (IRC), Mercy Corps and Save the Children said in a statement.

Nearly half the people living in Idlib have fled from their homes in other parts of the country, according to the UN, and many already depend on aid.

"If this deal falls short and military operations start, many hundreds of thousands will struggle to get the help they will so badly need," warned Lorraine Bramwell, IRC's Syria country director.