Syria rebels battle regime in Aleppo's fiercest fighting

Damascus

Two alliances of Syrian rebels battled to advance in government-held western Aleppo on Saturday, seizing an army barracks in one district but losing ground in others, in some of the fiercest fighting in the city since the conflict began.

US-led coalition forces, meanwhile, said they carried out a series of 16 airstrikes against the Islamic State group in their Syrian stronghold of Raqa, one of their biggest assaults on the extremists.

The announcement came hours after IS released a video showing teenage members executing 25 Syrian soldiers in an amphitheatre in the ancient ruins of Palmyra. Elsewhere, Syrian government forces launched a major operation to recapture Zabadani, the last opposition-held town in the Qalamun region near Damascus.

The Syrian Observatory for Human Rights, a Britain-based monitor, reported heavy clashes in several parts of western Aleppo, Syria's former economic powerhouse. It said fighters from the Conquest of Aleppo alliance of mostly moderate forces had captured a former research centre being used as a military barracks, opening up lines of attack against several nearby regime-held districts.

On Saturday, clashes raged around the complex as regime forces backed by airstrikes sought to recapture it, marking some of the worst violence in Aleppo since the Syrian conflict arrived in the northern city in mid-2012.

Conquest of Aleppo and a second rebel grouping, Ansar al-Sharia which is dominated by Islamists and Al-Qaeda's local affiliate Al-Nusra Front, began operations against government-held districts of Aleppo this week.