Rebel fighters near the wreckage of a Syrian aircraft downed Tuesday by a surface-to-air missile near Aleppo. An activist group says Jabhat al-Nusra, an al-Qaeda affiliate, carried out the attack. (Omar Haj Kadour/AFP/Getty Images)

A missile fired from rebel-held areas downed a Syrian reconnaissance plane on Tuesday, Syria’s military said, as a partial truce showed further signs of fraying. Activists said the aircraft was targeted by Islamist militants engaged in the ongoing clashes.

The aircraft was hit near the city of Aleppo, a front line in the fighting. The Syrian Observatory for Human Rights, a Britain-based monitoring group, said al-Qaeda-affiliated Jabhat al-Nusra took the pilot captive.

The state-run Syrian Arab News Agency, citing an unnamed military source, reported later that an aircraft on a surveillance mission was brought down with a surface-to-air missile and that the pilot ejected. Jabhat al-Nusra fighters have been suspected of using such missiles in past attacks.

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The reports of the plane downing suggest that Jabhat al-Nusra, which is seeking to claim new territory as it remains excluded from the truce, has an edge in firepower compared with other forces fighting the government, including some factions backed by the West. The incident could amplify calls from these rebel groups, which have heavy machine guns and other arms, to expand their arsenal to include such advanced weaponry as antiaircraft systems.

It is unclear what type of plane was shot down or how it was hit, but rebels claim to have downed the plane near the city of Aleppo. A fragile cease-fire has reduced some of the violence in Syria, but a recent uptick in fighting could threaten peace talks in Geneva. (YouTube/Halab Today)

A video posted on Facebook purported to show the plane’s wreckage and a mob around 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 escalated tensions in what has become a volatile proxy conflict involving world powers — with the West and its allies backing the rebels, while Russia and Iran support Syrian President Bashar al-Assad.

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Around Aleppo, a major northwestern city, opposition groups have attempted to seize areas from forces aligned with Assad.

In the northwestern province of Latakia, which borders Turkey, rebels and Jabhat al-Nusra militants have carried out attacks in recent days. Government forces, in turn, have been accused of numerous violations of the cease-fire, which 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 group.

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 civil war.

The wreckage of a government warplane reportedly shot down by al-Nusra, an al-Qaeda affiliate, over the northern Syrian town of Al-Eis on Tuesday. (Omar Haj Kadour/AFP/Getty Images)

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.

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The cease-fire serves as the basis for the talks and has received firm backing from Russia and the United States.

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

Hokayem noted that although violence has been reduced, a task force to monitor violations lacks an enforcement mechanism.

On Monday, a suspected 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 in Deir al-Asafir.

That airstrike drew condemnation from Western powers.

“This attack, which deliberately targeted civilians, including children, shows that the regime is continuing its abuses and violating the truce,” said a spokesman from the French Foreign Ministry, Romain Nadal.

Jabhat al-Nusra and the Islamic State militant group are excluded from the cease-fire and have been targeted independently by government forces, rebels and an international military coalition led by the United States.

Late last month, Syrian forces and allied fighters from Lebanon’s Hezbollah militia — backed by Russian air raids — captured the ancient city of Palmyra from the Islamic State, dealing a blow to the extremist group.

Zakaria Zakaria in Istanbul and Brian Murphy in Washington contributed to this report.