Opposition activists say Syrian government forces and rebels are waging a fierce battle near an airport in the northern Idlib province, on Wednesday, a day after similar clashes prompted officials to close the airport in Aleppo.
The Britain-based Syrian Observatory for Human Rights says rebels have launched an attack on a military airport near Taftanaz. The group says Islamist militant groups are involved in the fighting.
There was no immediate confirmation from the government, which has been battling opposition activists for almost two years.
On Tuesday, government aircraft pounded rebel-held areas of Aleppo, the country's commercial hub.
Authorities announced the closure of the city's airport because of rebel attacks.
Anti-government activists also reported heavy fighting in the Damascus suburb of Daraya, with bombings by Syrian warplanes.
Opposition groups say at least 75 people were killed in unrest across Syria on Tuesday.
Syrian rebels are trying to oust President Bashar al-Assad. Activists say 45,000 people have been killed in the conflict that began with peaceful anti-government protests in March 2011.