Syrian rebels have produced footage of a man they claim is the captured pilot of a fighter jet that went down in the east of the country.
The rebel Free Syrian Army (FSA) say they shot a military aircraft down near the Iraqi border.
But state media say the plane crashed because of “technical problems” and a search is under way to find the pilot.
Government forces have continued their advance in Aleppo, with reports of clashes in the west of the city.
According to Syria’s state-run news agency Sana, the plane that went down had suffered a fault with its “control mechanisms” during a routine training mission, forcing the pilot to abandon the aircraft.
The aircraft was shot down near the town of al-Muhassan, around 120km (75 miles) from the Iraqi border in Deir al-Zour province, the rebels say.
A group calling itself the “Revolutionary Youth of the Land of the Euphrates” uploaded a video to YouTube purporting to show the captured pilot surrounded by three armed rebels, saying that his mission was to “bomb the town of al-Muhassan”.
In the video, which cannot be independently verified, the seemingly middle-aged man identifies himself as a pilot, Col Fareer Mohammad Suleiman. He appears to have minor bruising to his face which he attributes to the plane crash.
Air power threat
In other footage provided by the rebels, what appears to be a Russian-built MiG-23 fighter jet is shown carrying two under-wing weapons pods thought to be loaded with air-to-ground missiles.
Anti-aircraft fire can be heard before the jet bursts into flames.
Rebel gunners are then heard on the footage celebrating.
The BBC’s Kevin Connolly, in neighbouring Lebanon, says that if the rebels have succeeded in downing a MiG-23, it would be a significant moment in the conflict.
Reports have emerged recently of anti-aircraft weapons reaching the rebels, and warplanes have been seen in recent weeks strafing and bombing targets in Aleppo.
Earlier this week, the rebels posted photos online showing them with a full surface-to-air missile system. This represents a potential threat to the regime’s air power, correspondents say.
Aleppo killings
In the purported pilot video, a rebel commander is heard saying that the captive will be treated according to the Geneva Convention for prisoners of war.
But further videos have appeared online that appear to show rebel killings in and around Syria’s second city, Aleppo.
Bodies are thrown from the roof of a post office and are then kicked by a crowd as they land on the ground. Another video shows a blindfolded man having his throat cut, although activists have denied rebel involvement.
According to activists, government forces have begun a new advance against rebels in Aleppo, which has seen fierce clashes between the two sides in recent weeks.
Troops entered the Saif al-Dawla neighbourhood with tanks and armoured vehicles, according to the UK-based Syrian Observatory for Human Rights.
The strategic southwestern district of Salah al-Din had been coming under bombardment since the morning, the Observatory said.
State media also said Syrian armed forces in central Homs province had killed a large number of “mercenary terrorists”.
But the activist Local Co-ordination Committees said the heaviest loss of life was in the capital, Damascus, and its suburbs where it reported 55 people killed.
Casualty numbers in Syria are almost impossible to verify because of the heavy restrictions placed on international journalists.