BEIRUT — Syrian government forces on Monday repelled a renewed rebel assault southwest of the city of Aleppo, forcing opposition forces to retreat from positions they seized a day earlier in the latest territorial back and forth between the two warring sides trying to break each other's hold around Syria's largest city.
The development followed intense and deadly battles around Aleppo and stepped up airstrikes by the Syrian and Russian air forces in Aleppo and nearby Idlib province.
The Islamic state group, meanwhile, claimed responsibility for a suicide bombing that struck a bus transporting rebels through a border crossing between Syria's opposition-held Idlib province and Turkey, killing more than 30 fighters.
The Atmeh border post is one of several crossings Syrian rebels use to bring in fighters and supplies. The Syrian Observatory for Human Rights said the death toll from the bombing rose to 32, expecting it to go even higher.
A media activist in the province who spoke on condition of anonymity for fear of retribution said some 200 rebels from various factions are based near Atmeh and regularly bring in weapons through the crossing.
The attempt to seize new ground around the city of Aleppo Sunday was spearheaded by a coalition of rebel and militant groups, including Syria's rebranded al-Qaida branch, which now goes under the name of Fath al-Sham.
Fath al-Sham was formerly known as the Nusra Front but recently changed its name and said it was severing ties with the global terror network in an apparent attempt to evade Russian and U.S.-led airstrikes targeting militants.
Fighting in Aleppo, once Syria's largest city and commercial capital, has intensified in recent weeks. The city near the Turkish border has been split between a rebel-held eastern part and a government-held western part since 2012. It has become the focal point of the war, encapsulating the bloody stalemate of Syria's conflict, now in its sixth year.
The rebel assault targeted key army positions at a cement factory southwest of Aleppo. Fath al-Sham posted video that purported to show militants pounding government positions with artillery and tank fire.
However, opposition activists and militant websites reported on Monday that the rebels and militants retreated from all positions they seized near the cement factory following a massive government counterattack.
The Britain-based Syrian Observatory for Human Rights, which monitors the war through a network of activists on the ground, said at least 35 rebels were killed in the fighting.
A Syrian military official said the Syrian air force launched "precise airstrikes on groupings and movements of terrorist groups south and west of Aleppo" that resulted in the death of dozens of "terrorists." The official spoke on condition of anonymity in line with regulations.
The Syrian government describes all armed groups fighting to topple President Bashar Assad as terrorists.
German Chancellor Angela Merkel's spokesman on Monday called on Russia, which is backing Assad, to exert its "great influence on the Syrian president" to alleviate the suffering in Aleppo.
Spokesman Steffen Seibert also criticized Moscow's offer of a daily three-hour cease-fire in Aleppo.
He said Russia's promise of three-hour cease-fires to allow humanitarian aid into Aleppo "is meant to sound like a concession, but is actually cynicism, since everyone knows that this time is nowhere near enough to really restore supplies to desperate people."