NEW YORK – 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. 

A handout picture released by the official Syrian Arab News Agency shows United Nations (UN) observers visiting the northeastern town of Hasaka on 29 July 2012.

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 neighboring Lebanon.

“The conditions to continue UNSMIS were not fulfilled,” France’s UN ambassador Gerard Araud said after a meeting on the conflict, referring to the mission whose mandate is due to end at midnight on 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 former 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 epicenter of the battle between the regime and armed rebels.

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

Mohammed Nur, director of the now closed Aazaz media center, 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.

With the violence showing no signs of abating, Russia – which along with China – has blocked three UN resolutions on the crisis, called for the UN to keep representatives inside Syria.

In a meeting with US Under Secretary of State Wendy Sherman, Russian Deputy Foreign Minister Gennady Gatilov emphasized “the need to maintain the UN presence in Syria,” the Foreign Ministry said in a statement.

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

Earlier Thursday, the Organization for Islamic Cooperation suspended Syria, with its chief Ekmeleddin Ihsanoglu saying: “This (Muslim) world can no longer accept a regime that massacres its people using planes, tanks and heavy artillery.”

The U.S. and the opposition Syrian National Council welcomed the move, but it was rejected by Syria’s staunch ally Iran and Damascus, which charged it was the victim of a U.S.-masterminded “conspiracy.”