A Syrian government delegation has arrived in Geneva to join a new round of UN-mediated peace talks with an umbrella opposition group that seeks to find a resolution to the country's five-year civil war.
The arrival of the Damascus team, led by Syria's UN ambassador Bashar Ja'afari, comes amid escalating fighting between government forces and insurgents in northern Aleppo which has killed 34 fighters on both sides over 24 hours.
The Britain-based Syrian Observatory for Human Rights said of those killed, 14 were pro-government fighters and 20 were militants, including members of Syria's al Qaida affiliate known as the Nusra Front.
The al Qaida branch and its more powerful rival, Islamic State, are not part of a ceasefire that came into effect at the end of February. The US and Russian-backed truce has held in most of Syria, except in the north, where it has practically collapsed.
The Nusra Front is deeply rooted in the areas in northern Syria controlled by opposition forces, complicating oversight of the truce.
IS militants have clashed with rival insurgents and pro-government forces in Aleppo, making a wide advance on opposition-held territory along the Turkish border, the Observatory said.
New York-based Human Rights Watch said Turkish border guards fired on hundreds of Syrian civilians fleeing the IS onslaught on Thursday and heading for a wall at the border. The rights group urged Ankara to allow thousands of Syrians fleeing to cross into Turkey to seek protection.
"As civilians flee Isis fighters, Turkey is responding with live ammunition instead of compassion," said Gerry Simpson, senior refugee researcher at Human Rights Watch.
"The whole world is talking about fighting Isis, and yet those most at risk of becoming victims of its horrific abuses are trapped on the wrong side of a concrete wall," he added.
Turkish officials said they were aware of the report but had no immediate response. There was no information whether any of the civilians were hurt in the shooting.
The latest IS advance has displaced 30,000 civilians north of Syria's largest city, Aleppo, the provincial capital.
The Syrian opposition High Negotiations Committee, which is negotiating in Geneva, has accused the Syrian government of more than 2,000 breaches of the ceasefire in deadly attacks on opposition areas.
UN special envoy Steffan De Mistura has said he hopes for a substantive round of "proximity talks" on a transitional government to end the war. The two sides do not actually talk to each other in Geneva but the UN envoy shuttles between them.
The most obvious public difference between the two sides revolves around the fate of President Bashar Assad. Opposition representatives have insisted that Assad be removed from power as part of any peace deal, while government officials have declared him to be a red line.
This round of talks began on Wednesday but the government said it was delayed because of parliamentary elections that were held this week in government-controlled areas of Syria. The opposition has dismissed the balloting as a sham and said it could further undermine the peace talks.