Syrian rebels have clashed with government forces at one of the country’s main crossings into Turkey, as the UN said the number of refugees who have fled the violence has surged to more than 170,000.

An army convoy was heading to the Bab al Hawa border when it was ambushed by opposition fighters. Footage appears to show rebels shooting at military tanks and helicopters.

Meanwhile, in the nearby city of Aleppo, Syrian jets continued to strike residential areas, reportedly killing a woman and three children.

Jets also bombed the town of Aazaz on Friday, just days after an air strike that flattened homes and killed at least 40 people, the Syrian Observatory for Human Rights said.

Fighting has also been reported in the central city of Homs and the southern city of Herak. The Syrian Observatory for Human Rights said 129 people were killed in violence on Friday alone.

The intensified fighting has sent thousands more Syrians fleeing into neighbouring countries, particularly Turkey, as the divided international community appears powerless to act.

More than 170,000 Syrians have sought sanctuary in Lebanon, Turkey, Jordan and Iraq – at least 12,000 of them in the last three days – leading to a growing humanitarian crisis, the UN said.

French foreign minister Laurent Fabius called for President Bashar al Assad’s regime to be “smashed fast” as he visited the largest of the refugee camps in Turkey.

“After hearing the refugees and their account of the massacres of the regime, Mr Bashar al-Assad doesn’t deserve to be on this earth,” he said.

Russia has rejected a proposal to set up no-fly zones to help fleeing civilians after the US said it was ready to consider the move.

“You have to solve citizen security issues using methods put in practice by international humanitarian law,” Russian foreign minister Sergei Lavrov told.

“But if you try to create no-fly zones and safety zones for military purposes by citing an international crisis – this is unacceptable.”

On Friday, veteran Algerian diplomat Lakhdar Brahimi, 78, took over as international envoy from Kofi Annan, who quit after the failure of his peace plan.

He was not confident he would be able to end the 17-month-old conflict, which the UN says has so far killed 17,000 people.

“I might very well fail, but we sometimes are lucky and we can get a breakthrough,” he said. “We have got to try. We have got to see that the Syrian people are not abandoned.”

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