Fighting is reported at several air bases in Syria as the rebels try to limit the regime's use of helicopters and jet fighters.
The government said on Saturday it had repelled an attack on an air base near Aleppo while rebels claimed victory at the Abu Zohur air base in Idlib province in the east of the country.
And another air force building in the eastern city of Deir al-Zour was seized, its commander killed and at least 16 personnel captured, according to the Syrian Observatory for Human Rights.
Footage posted on the internet showed captured regime officers and weapons.
It is impossible to independently verify the claims, as reporting by foreign journalists is severely restricted in Syria.
Russia said on Saturday that calls by the United Nations for the regime to stop using heavy weapons were naive.