Beirut (AFP) - More than a week of inter-rebel fighting in Syria's Turkish-held north has killed 58 people, mostly combatants -- battles that have allowed Al-Qaeda-linked fighters to gain ground, a war monitor said Tuesday.
The clashes since October 8 have been among the deadliest in years, killing 48 rebel fighters and 10 civilians, the Syrian Observatory for Human Rights said.
Fighting has taken place in a volatile area near the Turkish border.
Those killed include 28 fighters from the Hayat Tahrir al-Sham alliance (HTS), according to the Britain-based war monitor, which relies on a wide network of sources inside Syria.
The HTS alliance is led by Al-Qaeda's former Syria affiliate.
On Tuesday, Turkey deployed its forces near Azaz to act as a buffer between HTS and Turkey-backed forces, in its first major response to the fighting that erupted 10 days ago, according to the Observatory and an AFP reporter.
Dozens of rebel groups opposed to Syria's President Bashar al-Assad are confined to areas of northern and northwestern Syria, still evading government forces after more than a decade of war.
The latest fighting started this month between two rival pro-Turkish rebel groups, in the town of Al-Bab in Aleppo province.
It then spread to other areas, drawing in other factions -- including HTS.
'Alarmed'
HTS is widely seen as the strongest and best organised of the rebel factions and dominates the nearby Idlib region, Syria's last major opposition bastion.
Last week, the group captured the Afrin region from rival Turkish-backed rebels, advancing in the area for the first time since civil war broke out in Syria in 2011.
The United States condemned the HTS advance in a statement Tuesday.
"We are alarmed by the recent incursion of HTS, a designated terrorist organisation, into northern Aleppo (province)," the US statement read."HTS forces should be withdrawn from the area immediately".
HTS has leveraged the latest bout of fighting to expand its zone of influence, in a move green-lit by Turkey, which has never publicly backed it, the Observatory said.
"Hayat Tahrir al-Sham would not have entered the area without Turkey's consent," said Observatory chief Rami Abdul Rahman.
Since Monday, it has advanced towards the key town of Azaz, near the Turkish border further north, as persistent inter-rebel fighting has torpedoed a truce that briefly went into effect at the weekend.
Since 2011, the war in Syria has killed nearly half a million people and driven more than half of the country's pre-war population from their homes.
