A fighter jet has crashed in eastern Syria owing to "technical problems", according to state media.
The rebel Free Syrian Army (FSA) say they shot a military aircraft down in the same area, near the Iraqi border.
Experts who examined footage from the FSA of the downed plane say its camouflage and markings are consistent with those of a Syrian air force plane.
The pilot ejected and a search is now under way to find him, according to state media.
The plane had been on a "routine training mission", according to state-run news agency Sana.
It suffered a fault with its "control mechanisms", forcing the pilot to abandon the aircraft, Sana reported.
The aircraft was shot down near the town of al-Muhassan, around 120km (75 miles) from the Iraqi border, according to the rebels.
The FSA says that one of the two-man crew died and that another has been captured.
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".
Air power threat
Footage provided by the rebels shows what appears to be a Russian-built MiG-23 fighter jet carrying two under-wing weapons pods thought to be loaded with air-to-ground missiles.
Anti-aircraft can be heard before the jet bursts into flames.
Rebel gunners are then heard on the footage celebrating.
Reports have emerged recently of anti-aircraft weapons reaching rebels in Syria.
Earlier this week, photos were posted online by rebels showing them with a full surface-to-area missile system. This would pose a potential threat to the regime's air power, correspondents say.
Meanwhile, activists say that the government has begun a new advance against rebels in Aleppo, Syria's largest city. Aleppo has seen fierce clashes between the two sides in recent weeks.
Government forces entered the Saif al-Dawla neighbourhood with tanks and armoured vehicles, according to the UK-based Syrian Observatory for Human Rights.
The strategic northern district of Salah al-Din had been coming under bombardment since the morning, the Observatory said.