Rebels in eastern Syria said they had captured the pilot of a government fighter jet after shooting down his aircraft on Monday.
The downing of a warplane would be a rare event for lightly armed rebels faced with the superior weaponry of President Bashar Assad's forces. State television said the plane crashed due to technical difficulties.
In recent months the government has begun to use its air power to try to crush a 17-month-old uprising.
The state news channel Syria TV said the plane crashed due to technical problems during a "regular training mission" and a search party was under way. State news agency SANA said the pilot had ejected from the plane before it crashed.
Activists released a video on YouTube which they said showed the pilot, named in the footage as Colonel Mufeed Mohammed Suleiman.
Rebels who say they shot down the jet and captured Suleiman are shown questioning a greying, balding man. He is seated at a table in a black shirt next to several rebels in green camouflage uniforms and holding assault rifles.
"We will treat this prisoner according to what is required of us by our religion, our morals and the protocols in the Geneva Convention related to prisoners of war," a rebel identified as captain Abu Laith said.
The man said to be the pilot, who appeared calm, said the light bruises on his face were from the plane crash and not caused by the rebels, and that he had been given first aid.
An anti-Assad activist on Monday uploaded a separate video on YouTube, said to be from the town of Mohassen in Syria's eastern province of Deir al-Zor and showing a warplane streak through the skies amid heavy gunfire. The jet suddenly erupts into flames and begins to swirl, leaving a trail of smoke.
"God is greatest! A MiG fighter jet has been hit in the town of Mohassen," the activist shouts. There was no indication from the video as to whether the jet had been struck by rebel weapons fire.
It was also not possible to verify the location or date of the video.
An opposition source working with rebels in the area told Reuters the insurgents used anti-aircraft guns to down the jet.
"It was a MiG-21 brought down by a 14.5 anti-aircraft gun, the biggest in the rebel arsenal. The plane was flying too low and was within range. We have no information whether the pilot survived," the source said.
Rebels, whose armory is made up mostly of assault rifles, explosives and rocket-propelled grenades, have said they are unable to compete with the army's air power.
Fighter jets have been seen lately firing rockets on rebel-held villages and the northern city of Aleppo.
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