Fierce clashes have erupted near the international airport in Syria's second city of Aleppo, officials say.
State news agency Sana said the army was tackling rebels who had targeted airport operations. Unconfirmed reports say it has temporarily been closed.
There have also been air strikes on several suburbs of Damascus as the army battles Free Syrian Army rebels there.
Opposition groups say more than 44,000 people have been killed since Syria's unrest began in March 2011.
Damascus air strikes
The Free Syrian Army and government forces have clashed regularly over Aleppo since the rebels launched an offensive last July.
Sana reported that units of the Syrian army were clearing the areas surrounding the airport.
The rebels have targeted the airport to limit the movement of government forces to the city, which remains largely under rebel control.
One airport official told Agence France-Presse news agency the runways had been closed for a "very short period of time", adding: "There have been continued attempts by opposition militants to target civilian aircraft, which could cause a humanitarian disaster."
The UK-based opposition activist group, the Syrian Observatory for Human Rights, said it had been told that an explosion had hit a civilian plane taking off on Saturday, though it had no more details.
Elsewhere in Syria on Tuesday, air force jets struck rebel targets in the south-western Damascus suburb of Daraya.
Other air strikes were reported in eastern suburbs of the capital.
One resident of the the Old City district of Homs in central Syria told Reuters that there was shelling "from all sides" there.
The Syrian Observatory for Human Rights also reported fighting in the north-western province of Idlib.
The latest violence comes after United Nations peace envoy Lakhdar Brahimi warned on Saturday of "hell" for Syria if no political solution was negotiated to the crisis.
Mr Brahimi said the conflict had become more militarised and sectarian.