Fighters in Syria's Idlib have failed to meet a deadline to leave a planned buffer zone around the country's last rebel bastion as set out under a Russian-Turkish deal.
The armed groups were supposed to withdraw from the buffer on Monday as a final condition to implementing a Russian-Turkish agreement to stave off a Syrian government offensive on the northwestern region of Idlib.
The accord hung in the balance early Monday, seven years into a grinding civil war that has killed hundreds of thousands of people and displaced millions.
Just hours before the deadline expired, rebels vowed to continue to fight.
"We have not abandoned our choice of jihad and fighting towards implementing our blessed revolution," said Hay'et Tahrir al-Sham (HTS), an alliance led by al-Qaeda's former Syrian affiliate.
"We appreciate the efforts of all those who strive inside and abroad to protect the liberated area," it said in an apparent reference to Turkey.
"But at the same time, we warn of the deceitfulness of the Russian occupier," it said of President Bashar al-Assad's ally.
Under the deal, heavy weapons were to have been withdrawn from the horseshoe-shaped buffer by October 10 and fighters to have left by Monday.
Looking for a fight?
The Syrian Observatory for Human Rights said it had not observed any fighters leaving the outlined demilitarised area by the time midnight struck.
"The jihadists not withdrawing gives the regime and Russia an excuse to carry out a military operation at least within the demilitarised zone," Observatory head Rami Abdel Rahman said.
HTS likely "tried to gain time by neither explicitly refusing nor accepting the deal" between Russia and Turkey, he said.
Late Saturday, "heavy mortar shells" were fired from the planned buffer area into regime territory, killing two soldiers, according to the Syrian Observatory.
Rebels reportedly fulfilled the first part of the deal, with Turkish officials, armed factions, and the Observatory reporting the area was free of heavy weaponry.
But the mortar fire that hit an army position in Hama province appears to have violated the accord.
It was unclear which groups fired the mortars late Saturday as both the Turkish-backed National Liberation Front and rival factions were present in the area. The NLF holds about half of the Idlib region and has welcomed the accord.
The lion's share of Idlib is held by Hay'et Tahrir al-Sham, as well as more hardline fighters such as Hurras al-Deen and Ansar al-Islam.
Those groups also control more than two-thirds of the planned buffer zone and were supposed to withdraw by Monday.
Hurras al-Deen has publicly rejected the agreement, although it apparently withdrew its heavy arms from the area last week.
HTS, widely considered the most powerful force in Idlib, had quietly abided by the deal's first deadline and re-stationed heavy arms elsewhere.
But getting the group to agree to the second part of the deal has proven more difficult.
In a recent report for the Turkey-based Omran Center, analyst Nawar Oliver described HTS's approval as the deal's ultimate "test".
"If HTS acts as a spoiler to the agreement on the ground, this will probably lead to one of two scenarios: either Turkey and the NLF launch military action against HTS, or Russia will seize the opportunity with the support of the regime and its allies to enter Idlib," Oliver said.
"The ramifications of that move could be vast," he added.
Al-Assad and other top government officials have warned the Idlib deal was only a "temporary" measure.
On Friday, residents around Idlib received warning messages on their mobile phones from the Syrian army. "Get away from the fighters. Their fate is sealed and near," one said.
The agreement signed on September 17 averted a large-scale offensive, which the United Nations had said could cause massive displacement and bloodshed.
The UN warned that such action would provoke a humanitarian disaster in the region, where as many as 800,000 people - half of whom are internally displaced from previous offensives - could be forced to flee again by a regime assault on Idlib and surrounding areas.
Nearly three million people live in the zone now, hundreds of thousands of them already displaced by the brutal seven-year war and others heavily dependent on humanitarian aid to survive.