A video issued by Syrian rebels purports to show a captured pilot who ejected from a warplane they claim they shot down.
The authenticity of the video shown on the pan-Arab network Al-Arabiya could not be independently confirmed, but it comes amid conflicting accounts over the MiG fighter.
Rebels claim they shot down the plane over eastern Syria. The Syrian government says a warplane experienced malfunctions and the pilot was forced to eject.
If the rebel claim proves true, it could mark a significant jump in their ability to combat widening air attacks from President Bashar Assad's forces.
In the video, a man identifies himself as the pilot as he is surrounded by three armed men. He says he has been treated well and urges officers to defect from Assad's military.
Earlier Monday, activists released a video which they claimed shows a government Soviet-made MiG warplane catching fire after it apparently was hit by ground fire over Deir el-Zour province. The warplane appears to be spiralling into a ball of flames. It was impossible to independently verify the video.
SANA news agency said the plane was on a training mission when a "technical failure occurred" and the pilot had to eject. It added that a search was under way to find the pilot.
Also Monday, Syrian diplomat working at the United Nations in Geneva joined his country's opposition after deciding he can no longer represent Assad's regime.
A spokesman for the UN Human Rights Council, Rolando Gomez, identified the Syrian as Danny al-Baaj and described him as a junior member of his country's UN mission.
Syria is not a member of the 47-nation council, but al-Baaj worked with it as part of his duties. The uprising in Syria has been a major concern of the council since starting in March 2011.
A growing number of Syrian officials have switched to the opposition as the months have worn on.
Al-Baaj's family said he decided several days ago he could no longer represent Assad, but has not determined his next move.
Pilot reportedly captured alive
If the rebels indeed managed to shoot down a fighter jet, it would mark a major leap forward in their military capabilities as well as a big blow to the regime, which started using its air force intensively in the civil war over the past weeks.
The Britain-based activist group Syrian Observatory for Human Rights said the plane was hit as it was conducting air raids on the town of Muhassan. The group quoted activists in the area as saying the plane was hit with fire from a heavy machine-gun used by rebels in the area.
Observatory Director Rami Abdul-Rahman said he was told by locals that the rebels captured the pilot, a colonel, alive.
Theodore Karasik, a regional security expert at the Dubai-based Institute for Near East and Gulf Military Analysis, said the rebel claim — if true — would suggest a stepped-up flow of outside military assistance. Older anti-aircraft weapons, possibly looted from Syrian arsenals such as variations on the Soviet-era SA-7, are considered overmatched by later model MiGs in the Syrian air force.
"If this is true, the conjecture would be that covert aid to the rebels is expanding with higher-grade anti-aircraft capabilities," he said.
Calls for no-fly zones
Gulf states such as Saudi Arabia and Qatar have pledged to help supply the Syrian rebels, but the extent of the aid is unclear. Rebel commanders have consistently complained about lack of ammunition, including during recent battles in Aleppo. Last week, anti-regime protesters across Syria staged rallies calling for greater anti-aircraft firepower.
On Sunday, the head of Syria's main opposition group in exile called for international powers to impose a no-fly zone in border areas to protect civilians who are coming under increasingly intense attacks by regime warplanes and helicopters.
The president of the Syrian National Council, Abdelbaset Sieda, told The Associated Press that such a move by the international community would show President Bashar Assad's regime that his opponents around the world are serious.
The Syrian opposition has been calling for a no-fly zone over Syria for months. But Sieda renewed the plea a day after U.S. Secretary of State Hillary Rodham Clinton said Washington and Turkey were discussing a range of steps including a no-fly zone over some parts of Syria as the regime increasingly uses its air force to attack rebels.
The eastern, oil-rich region of Deir el-Zour near the border with Iraq has been witnessing heavy clashes between government troops and rebels over the past week. Syrian Prime Minister Riad Hijab, who defected to Jordan earlier this month, comes from Deir el-Zour.
Cameraman believed to be dead
The toll of Syria journalists killed over the weekend rose to three on Monday, when a pro-government TV station said one of its cameramen kidnapped three days ago is believed to be dead.
The station said two other journalists and their driver are being held by rebels near the capital Damascus.
The station said gunmen kidnapped the cameraman Friday along with three other employees of the pro-regime Al-Ikhbariya TV while covering the violence in the Damascus suburb of al-Tal. The three surviving members of the team appeared in an online video, saying they were being held by rebel forces who were treating them well.
A man who identified himself as a rebel spokesman also appeared in the video, saying the cameraman and two members of the Free Syrian Army rebel group were killed in government shelling while on a tour in al-Tal to shoot destruction in the area.
It was impossible to independently verify the events shown in the video. But the general manager of Al-Ikhbariya TV said they believe the cameraman is dead. In June, gunmen raided Al-Ikhbariya's headquarters, killing seven employees.
Two other journalists were killed in Damascus or its suburbs on Saturday. A reporter for state-run news agency SANA was killed in his Damascus home, while another working for the pan-Arab Al-Arabiya TV was killed in a blast in al-Tal.
Activists reported clashes and shelling between government troops and rebels in areas including Damascus and its suburbs, the central province of Homs, and the southern region of Daraa. The Observatory said 52 people were killed so far Monday, 39 of them civilians while the others were soldiers or rebels.
Activists say more than 20,000 people have been killed since the revolt began in March 2011.