Syrian rebels on the attack, according to unverified footage.
This video from a social media website, purports to show rebels battling to capture a key government air base near Aleppo on Wednesday.
A monitoring group said the attack at Taftanaz was indeed underway.
The Syrian Observatory for Human Rights claimed the rebels forces were made up fighters from the al Qaeda-linked al-Nursa Front and the Ahrar al-Sham Brigade, rmaking another attempt to capture the base.
The future of the conflict may turn on air power.
The lightly armed rebels have made gains over recent months but have faced increasing use by President Bashar al-Assad's forces of attack jets and helicopters - this is unconfirmed activist footage of government jets in action over Damascus last week.
No surprise the rebels have turned their attention to air bases.
There was no mention of the Taftanaz battle on Syrian government controlled media -- and restrictions on independent journalists make reports hard to verify.
The attack comes against the gloomy backdrop of the latest estimate in numbers of dead.
The United Nations now says more 60,000 people have died since Syria's uprising began almost two years ago.