Heavy fighting for control of the international airport in the northern Syrian city of Aleppo and a major military air base nearby has killed some 150 rebels and government soldiers over the past two days, activists say.
The director of the Britain-based Syrian Observatory for Human Rights, Rami Abdul-Rahman, said the casualties are almost evenly divided between opposition fighters and troops loyal to President Bashar Assad.
Rebels launched a major attack on Aleppo's civilian airport and the adjacent Nairab airfield on Wednesday. So far, they have captured most of the "Brigade 80" base, responsible for protecting the area, as well as an army checkpoint. The airport itself and the military airfield, which have their own defences as well, both remain in regime hands.
Today, the Observatory and the Local Co-ordination Committees activist group said rebels and President Bashar Assad's forces were shelling each other in renewed clashes.
"The operation will continue until we control the airport and Nairab," Col. Abdul-Jabbar al-Aqidi, commander of the rebels' Military Council in Aleppo, told Al-Arabiya TV.
Control of Aleppo international airport and Nairab would be a huge strategic shift for Syria's north-eastern region, giving the opposition a potential air hub enabling aid and other flights.
But to start using the airport, the rebels first would likely have to secure all of the embattled city of Aleppo, where fighting has settled into a bloody stalemate in the streets and squares, as well as much of the surrounding countryside.
Although Mr Assad's regime does not appear on the brink of collapse, rebels seeking to remove him have scored a string of strategic victories over the past week, seizing a large dam, a smaller air base in Aleppo province and an oil field in the east. These and other blows have shrunk the portion of the country that Mr Assad effectively governs and could deprive his regime of resources necessary for its survival.
In recent weeks, opposition fighters have also been trying to slowly push their way into the capital, Damascus. Today the Observatory reported shelling and fighting in the Damascus suburbs of Zabadani and Daraya, where a number of soldiers were killed or wounded when their vehicle received a direct hit.
It said rebels and troops fought in the eastern city of Deir el-Zour and that opposition forces control most of it. It added that government forces bombardment of the northern town of Khan Sheikhoun killed 11 people including a child.