Government forces battled with rebels and al-Qaida militants on two fronts in Syria on Sunday as the country prepared to close out another violent year since the country descended into civil war in 2011.

Rebels supported by an al-Qaida-linked cell renewed their assault against pro-government forces that have been holding a vast pocket of the Damascus suburbs under siege, said the Britain-based Syrian Observatory for Human Rights. A second front between many of the same groups saw fresh fighting in northwest Syria, along the border between Idlib and Hama provinces, according to the Observatory and Syrian military media.

The fighting outside Damascus was concentrated around the contested town of Harasta and a nearby military installation. The insurgents flanked the installation on Sunday, trapping an unknown number of pro-government forces inside, reported the Observatory. The local, activist-run Ghouta Media Center reported fierce clashes and dense government airstrikes.

Twenty-one soldiers and 26 rebels and al-Qaida fighters were killed in two days of clashes, according to the Observatory’s director, Rami Abdurrahman.

Rebels first attacked the installation seven weeks ago. The government responded with waves of indiscriminate air strikes and artillery attacks that killed more than 250 civilians in what are called the eastern Ghouta suburbs of Damascus, which are still under rebel control.

The Syrian Civil Defense search-and-rescue group, also known as the White Helmets, said shelling and rocket fire killed 19 people in eastern Ghouta on Saturday, one day after medical evacuations were completed to save the lives of 29 others. The Red Cross and Red Crescent took three days to evacuate 29 patients from the besieged suburbs to receive urgent medical care at government hospitals in Damascus.

The U.N. says government forces are holding 400,000 people under siege in eastern Ghouta. The region was once a hotbed of protest against President Bashar Assad’s government. The subsequent crackdown on demonstrations in Ghouta and other parts of the country in 2011 sparked the ongoing civil war that has killed more than 400,000 people and displaced half of Syria’s population.