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 daily earlier, the Syrian government and activists said.
The development followed intense battles between the two sides, and comes amid suggestions that Russia -- Syrian President Bashar Assad's most powerful backer -- could "start fighting together" with the U.S. against the rebels who hold vast swathes of the sprawling city under siege.
The attempt to seize new ground around the northern city was spearheaded by a coalition of rebel and militant groups, including Syria's rebranded al-Qaeda 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 U.S. and European nations have pushed Russia for weeks to cajole Assad to agree to some negotiated truce in Aleppo, and on Monday Russian Defense Minister Sergei Shoigu was quoted as saying Moscow and Washington "are moving step by step closer to a plan - and I'm only talking about Aleppo here - that would really allow us to start fighting together to bring peace so that people can return to their homes in this troubled land."
"We are now in a very active phase of negotiations with our American colleagues," Shoigu said, according to Russia's RIA news agency.
In Washington, however, State Department officials told CBS News correspondent Margaret Brennan there was nothing to announce yet. Direct talks are ongoing with the Russians in Geneva and there is no "deadline" for any agreement on cooperation, but the hope is to get something nailed down before President Obama and his Russian counterpart Vladimir Putin meet in early September.
The outlines of any intelligence sharing deal remain the same, says Brennan: Russia would need to get Syria to ground its air force for a few weeks before the U.S. begins sharing intel on al Qaeda-linked rebels with Moscow.
The rebel assault, which began Sunday, 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 Assad as terrorist.