Idlib (Syria) (AFP) - Syria's army Friday warned residents of the country's last major rebel bastion to stay away from jihadists, who have yet to withdraw from a buffer zone ahead of a looming deadline.

Regime ally Moscow and rebel backer Ankara agreed last month to set up a demilitarised area around the northwestern region of Idlib to stave off a major regime offensive on a region that hosts some three million people.

The U-shaped zone aims to avert one of the worst humanitarian crises in Syria's seven-year war.

But jihadists, who under the deal must withdraw from 15- to 20-kilometre (nine- to 12-mile)-wide buffer zone by Monday, have not yet shown any sign of leaving.

Residents in the area received warning messages on their mobile phones from the Syrian army early Friday, an AFP correspondent said.

"Get away from the fighters. Their fate is sealed and near," one said.

"Don't allow the terrorists to take you as human shields," said another, addressed to residents of the planned buffer zone.

Idlib's dominant force -- an alliance led by Al-Qaeda's former Syria affiliate -- and other jihadist factions control more than two-thirds of the planned zone.

- 'Fears of violence' -

But the Hayat Tahrir al-Sham (HTS) alliance has not yet officially responded to the deal, and a Britain-based war monitor said on Friday that no jihadists had left the planned buffer area.

"There has been no withdrawal of any members of the jihadist factions with their light weapons," the Syrian Observatory for Human Rights monitoring group said.

A rebel source inside the zone told AFP he had seen no HTS combattants leave.

"We have not observed any withdrawal of fighters," he said.

Other jihadists in the planned buffer zone include the Turkestan Islamic Party and current Al-Qaeda outfit Hurras al-Deen.

Turkey-backed rebels and jihadists met an initial deadline on Wednesday to remove their heavy weaponry from the buffer strip.

But it is not clear what will happen if the second and final October 15 deadline is not met.

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On Friday, Amnesty International called on Russia, Turkey and fellow regime backer Iran to "prevent another humanitarian catastrophe in Idlib".

Four international aid groups working in Idlib warned that failure to implement the deal could trigger renewed violence and 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.

- Mass displacement? -

"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 of the people living in Idlib have fled there after being displaced from other parts of the war-ravaged country, according to the United Nations.

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.

Forces loyal to President Bashar al-Assad have retaken large parts of Syria from opposition fighters and jihadists since Russia intervened in the war in September 2015.

After a series of victories near Damascus and in the south of the country earlier this year, a similar Moscow-backed assault had been expected against Idlib before the Russia-Turkey deal was announced.

Despite progress in implementing the accord, Assad insisted on Sunday it was a "temporary measure" and that Idlib would eventually return to state control.

The Syrian war has killed more than 360,000 people since it erupted in 2011 with the brutal repression of anti-government protests.