Syrian troops have recaptured parts of a military base seized by rebels earlier this year in a fierce fighting near Aleppo international airport, activists say.
Heavy fighting erupted in the early hours of Friday around Base 80 outside Syria's main northern city.
A fighter near the airport called the army offensive the heaviest barrage in more than a year on rebel-held areas near the airport.
"We did not see it coming. The attack came as a real shock to us" he told Al Jazeera.
"There is an insane campaign going on. The regime is employing a scorched-earth policy."
Initial reports suggested both sides had suffered casualties in the fighting. The UK-based Syrian Observatory for Human Rights added that towns near the base had come under heavy bombardment, along with neighbourhoods of Aleppo city.
"Regime troops have advanced inside the base and now control large parts of it, and rebel groups and the Islamic State [of Iraq and the Levant] are bringing in reinforcements," said the Observatory.
Rebel forces seized control of Base 80 in heavy fighting in February. The base's garrison was responsible for securing Aleppo international airport and the adjacent Nayrab military airfield, which both remain under regime control.
Elsewhere, the Observatory reported ongoing fighting around a key weapons depot near the town of Mahin in central Homs province.
Rebel groups seized control of part of the depot earlier this week, and the Observatory said the army and opposition were bringing in reinforcements.
More than 120,000 people have been killed in the conflict in Syria since March 2011, according to the Observatory. Millions more have been internally displaced or have fled abroad.