BEIRUT — Fierce clashes erupted between rebels and pro-government forces around Syria’s largest city, Aleppo, Saturday despite a proclamation from the Syrian military that it would extend its own cease-fire through Monday.

The military had declared a nationwide cease-fire for the Eid al-Fitr holiday July 6, expiring July 8 at midnight, but it had little impact on the ground, as pro-government forces choked off the last supply route to opposition areas in the contested city of Aleppo on July 7.

On Saturday evening, rebels launched a counteroffensive, leading with two car bombs to open the vital Castello road to eastern Aleppo, according to activists. The Britain-based Syrian Observatory for Human Rights monitoring group, which gathers information from a network of informants across the war-torn country, said the cars were driven by two suicide bombers from al-Qaida’s Syria affiliate, the Nusra Front, which fights alongside rebel groups against government forces. Syrian journalist Ahmad Primo said one of the car bombs was driven by a militant from Ahrar al-Sham, another ultraconservative jihadist group fighting the government.

Rebels then launched a ground offensive on the government’s newly acquired positions overlooking the supply route, according to the social media accounts for the Aleppo Conquest Operations Room and Levant Front, two rebel coalitions. Fighting for the Mallah farms continued into the night.

Two Russian airman, meanwhile, were killed in the country’s central Homs province when their helicopter was shot down by Islamic State fighters, according to Russia’s Defense Ministry. The Russian-Syrian government military alliance has had trouble securing the country’s desert interior after forcing the extremist group out of the ancient city of Palmyra in March. Islamic State militants promptly seized the nearby Shaer natural gas fields after that, and threatened to advance on Palmyra once again.

A Defense Ministry statement on Saturday reported by the state news agency Tass said the incident occurred Friday east of Palmyra.

According to the statement, the two Russians were making a test flight in the Homs region with a Syrian Mi-25 helicopter that was carrying ammunition. It said fighters from the Islamic State group, which is also known as ISIS or ISIL, broke through Syrian forces’ lines east of Palmyra at the same time.

The statement said the Syrians requested the crew help strike the Islamic State fighters and the helicopter was shot down after the crew exhausted the aircraft’s ammunition and were leaving the scene.

The clashes north of Aleppo, for Castello road, followed a bloody 24 hours for residents inside the divided metropolis. State media reported that a rocket barrage on residential areas on the government side of the city killed 44 people Friday night. The Observatory put the toll at 38 dead, among them 14 children and 13 women. The Observatory said another nine people, including eight women and children, were killed in presumed Russian or Syrian government airstrikes and rocket attacks on the opposition-held side of the city.

U.N. deputy spokesman Farhan Haq said in New York on Friday that the Office for the Coordination of Humanitarian Affairs is “extremely concerned at the unfolding situation in Aleppo, Syria, particularly the situation for the estimated 300,000 people trapped in the eastern part.”

Haq noted the heavy clashes along Castello road, the only route to the rebel-held part of Aleppo.

Elsewhere in Syria, airstrikes on the village of Darkoush in the rebel-held northwestern province of Idlib on Friday killed 23 people, including two children, according to the Observatory. It was not clear whether Syrian or Russian warplanes were responsible.

The now-extended cease-fire is set to expire at midnight on July 12.

State media acknowledged the fighting outside Aleppo, saying troops were targeting “terrorists,” the government’s catch-all term for the armed opposition.