A Syrian fighter jet has crashed in eastern Syria, state television said, hours after rebels said they had brought down a jet in the same area.
The official news channel Syria TV said the plane crashed due to technical problems during a "regular training mission".
State news agency SANA said the pilot had ejected from the plane and a search operation was under way.
In recent months the government has begun to use its air power to try to crush a 17-month-old uprising.
Anti-Assad activists uploaded videos on YouTube of what they claimed is footage from the town of Mohassen in the eastern province of Deir al-Zor showing a warplane streak through the skies amid heavy gunfire.
In the footage, the jet suddenly erupts into flames and begins to swirl, leaving a trail of smoke.
Rebels, whose armoury 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.
Elsewhere, United Nations humanitarian chief Valerie Amos is to go to Syria tomorrow to discuss ways of increasing emergency aid to civilians caught up in the conflict there.
Ms Amos will also visit Lebanon, where she will meet Syrian families who have fled the fighting and hold talks on providing support to the growing number of refugees.
The humanitarian situation in Syria has worsened in recent weeks.
"Two million people are now estimated to have been affected by the crisis and over one million have been internally displaced," the UN said.
Nearly 150,000 Syrian refugees have registered in Iraq, Jordan, Lebanon and Turkey since the conflict began 17 months ago.
Ms Amos was last in Syria in March to seek unhindered access for aid workers to the worst-hit areas.
She secured an agreement from the government for a joint but limited assessment of the humanitarian situation in the country.
The UN has been trying to expand aid operations in Syria, but despite growing needs, the authorities have refused to grant visas to Western aid workers.
Growing insecurity forced the UN to withdraw some expatriate aid workers from Syria in late July.
The world body has relied on the Syrian Arab Red Crescent to distribute its aid supplies, including food rations to 542,000 people in July, falling well short of its target of 850,000.
