A member of the Free Syrian Army opens fire on a government forces helicopter flying

AFP

The United Nations called an end to its observer mission in Syria on Thursday, while activists reported more bloodletting in an attack on civilians in the main battleground of Aleppo.

The UN decision was announced as the international community piled the pressure on President Bashar al-Assad's embattled regime to end 17 months of fighting that is now threatening to entangle neighbouring Lebanon, reports AFP.

"The conditions to continue UNSMIS were not fulfilled," France's UN ambassador Gerard Araud said after a New York meeting on the conflict, referring to the mission whose mandate is due to end at midnight Sunday.

Major powers have long been at odds how to end the increasingly brutal battle for Syria, and the withdrawal of the observers follows the collapse of a peace plan drawn up by outgoing peace envoy Kofi Annan.

On the ground, activists reported that Syrian forces shelled a group of people queuing outside a bakery in the eastern Qadi Askar district of Aleppo, the city at the epicentre of the battle between the regime and armed rebels.

The Syrian Observatory for Human Rights said 10 people were killed in the district, and that at least 99 had died in violence across the country on Thursday, most of them civilians.

On Wednesday, around 40 people, including women and children, were killed in a massive air strike on civilians in the rebel bastion of Aazaz, just north of Aleppo, according to rights groups and residents.

Human Rights Watch urged the UN Security Council to impose an arms embargo on Syria after the air strike on Aazaz. "Yet again, Syrian government forces attacked with callous disregard for civilian life," it said.

Mohammed Nur, director of the now closed Aazaz media centre, said 40 people were killed -- including 30 from one extended family -- and 150 wounded but that bodies were still being returned from nearby Turkey where many of the victims had fled to.

"Bashar al-Assad doesn't care where the bombs land and in any case, his pilots are not that accurate," he said.

With the violence showing no signs of abating, Russia -- which along with China -- has blocked three UN resolutions on the crisis, called for world powers to make a joint appeal for the regime and rebels to end the fighting.

Chinese Foreign Minister Yang Jiechi also urged a visiting Syrian envoy to implement a ceasefire and accept international mediation.

But French Foreign Minister Laurent Fabius renewed calls for Assad to go.

"France's position is clear: we consider Assad to be butchering his own people. He must leave, and the sooner he goes the better," Fabius said at a refugee camp for Syrians in Jordan, before flying on to Lebanon.