Rebel fighters and civilians gather around the wreckage of a warplane that was reportedly shot down in the Talat al-Iss area, south of Aleppo, Syria April 5, 2016. REUTERS/Ammar Abdullah (Ammar Abdullah/Reuters)

Rebels in northern Syria downed an apparent warplane on Tuesday, according to a monitoring group and activists, as a partial truce showed further signs of fraying.

The aircraft caught fire and crashed near the city of Aleppo, according to the Syrian Observatory for Human Rights, a Britain-based monitoring group. The origin and make of the plane were not clear, although jets from Syria’s government and Russia are suspected of carrying out bombing raids in the area.

A video posted on Facebook purported to show the wreckage and an angry mob surrounding the pilot, who apparently survived. The video’s authenticity could not be independently verified.

In November, Turkey shot down a Russian warplane over Syria, an incident that dramatically escalated tensions in what has become a volatile proxy conflict for world powers — with the West and allies backing rebels, while Russia and Iran support the forces of Syrian President Bashar al-Assad.

Civilians carry a piece of a warplane brought down in the Talat al-Iss area, south of Aleppo, Syria April 5, 2016. REUTERS/Ammar Abdullah (Ammar Abdullah/Reuters)

In recent days, rebel forces have fought intense battles alongside militants from al-Qaeda’s affiliate in Syria, Jabhat al-Nusra, near Aleppo and in a northwestern province that borders Turkey.

The opposition groups have attempted to seize a number of villages from forces aligned with Assad’s government, which in turn has been accused of numerous violations of the nationwide cease-fire that took hold Feb. 27.

“Our attacks are a response to ongoing regime violations of the truce,” said Ahmed Haj Ali, a spokesman for the 1st Coastal Division, a rebel outfit affiliated with the umbrella Free Syrian Army.

The worsening violence could threaten the momentum of talks in Geneva that resumed last month as part of a renewed international effort, led by Russia and the United States, to end Syria’s devastating civil war.

The first round of those negotiations ended last month on a relatively positive note. Staffan de Mistura, the U.N. envoy to Syria and mediator for the talks, plans to reconvene with government and opposition delegations in the Swiss city this month.

“We are all surprised at how long this cessation of hostilities has lasted, but it still contains profound flaws and ambiguities,” said Emile Hokayem, a Middle East analyst at the London-based International Institute for Strategic Studies.

“But the fighting has not stopped.”

The cease-fire, which serves as basis for the talks, has received firm backing from both Russia and the United States even as the powers support opposing sides in the conflict. But while violence has been reduced, a task force to monitor violations, jointly chaired by Moscow and Washington, lacks an enforcement mechanism, Hokayem said.

Warring parties have repeatedly flagged alleged violations, which still are committed daily, especially by government forces, analysts and Syrian rebels say.

Over the weekend, an apparent Syrian government warplane bombed a hospital in Azaz, a rebel-held town near the Turkish border.

Last week, government aircraft bombarded a rebel-held suburb of the capital, Damascus, killing more than 30 people, according to monitoring groups and activists.

The Syrian Observatory for Human Rights said 12 children and one emergency responder were among those killed in the attack on the Eastern Ghouta town of Deir al-Asafir.

That incident drew strong rebukes from Western powers, particularly from French Foreign Ministry spokesman Romain Nadal.

“This attack, which deliberately targeted civilians, including children, shows that the regime is continuing its abuses and violating the truce,” said Nadal, who condemned the Syrian government.

It is unclear how these apparent violations are being dealt with.

Meanwhile, Jabhat al-Nusra appears to be acting as a spoiler. The al-Qaeda affiliate, along with the Islamic State militant group, is not a party to the partial cease-fire and has come under attack by government warplanes.

In turn, Jabhat al-Nusra fighters on Saturday carried out attacks in an area south of Aleppo in an apparent bid to seize territory.

Even though they support the cease-fire, rebels aligned with the Western-backed Free Syrian Army joined the al-Qaeda-linked militants in the attacks near Aleppo and in the northwestern Latakia province. The attacks in along the border areas in Latakia targeted at least four villages seized recently by pro-government forces with the help of air raids by Russia.

FSA-aligned groups have not publicized involvement in those attacks, suggesting to some analysts that they are participating in them to restrain Jabhat al-Nusra. The rebels do not want the al-Qaeda-linked group to seize territory at their expense.

Zakaria Zakaria in Istanbul contributed reporting

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