The airport, near the town of al-Boukamal along the border with Iraq, has been turned into a military base. Rebels have been making advances in the town for weeks, seizing control of the military security building and a checkpoint at the edge of al-Boukamal earlier this week.
The rebels have captured swaths of land and several strategic installations, particularly along the border with Turkey, but they are outgunned by the regime in battles to hold on to them. The Syrian military has relied on air power to reverse the rebel gains.
In Tehran, Iranian Foreign Minister Ali Akbar Salehi warned that providing opposition groups with heavy arms could put the entire region at risk of "organized terrorism." He was responding to a move in Europe to cancel an arms embargo.
He said that arming Assad's opponents, as Damascus accuses Qatar and Saudi Arabia of doing, violates international law and principles of nonintervention in domestic affairs.
"Unfortunately, now some reports have been published saying some sides are intending to send semi-heavy and heavy arms for the opposition groups openly," Salehi said at a conference to reconcile Syria's government with some Syria-based opposition factions which are tolerated by the regime.
Iran has backed Assad in the conflict. Iran, Russia and China are Syria's main allies.
The conference is seen as a response to last week's meeting in Qatar, where opposition groups formed an umbrella coalition against Assad.
So far, France is the only Western country to recognize the Doha-formed Syrian National Coalition for Opposition and Revolutionary Forces. Other EU nations and the United States and have said they prefer to wait to see whether the coalition represents the variety of people in Syria before they recognize it.
Associated Press writers Barbara Surk in Beirut and Nasser Karimi in Tehran, Iran contributed to this report.