Updated

UN chemical weapons experts, in Syria to investigate alleged use of the banned arms, on Sunday left their Damascus hotel to carry out a new mission, an AFP photographer said.

The experts, who arrived in the Syrian capital last Wednesday on their second visit in two months, headed out on board four UN vehicles.

The United Nations has said the experts are investigating seven alleged chemical weapons attacks and expect to wind up their work on the ground on Monday.

They hope to have a comprehensive report ready "by late October".

The UN mission is separate from a team of Organisation for the Prohibition of Chemical Weapons inspectors due to start work in the coming days to destroy Syria's chemical arsenal.

The alleged attacks being probed include a March 19 incident in Khan al-Assal, in Aleppo province of northern Syria, that both the regime and rebels reported, each accusing the other of responsibility.

Other sites being investigated include the Sheikh Maqsud neighbourhood of Aleppo city, allegedly the site of an April attack, and Saraqeb in the northwest province of Idlib on the border with Turkey.

The team is also continuing investigations into an August 21 attack in the suburbs of Damascus that coincided with their first mission to Syria last month.

The UN experts visited the site of that alleged attack during their first trip and have issued a preliminary report confirming the use of the nerve agent sarin in the area.

In addition, the team is investigating three subsequent alleged attacks -- on August 22 in Bahhariyeh, near Damascus, on August 24 in the Jubar district of the capital, and a seventh incident reported in Ashrafiyeh Sahnaya, Damascus province, on August 25.

"In the course of performing their task, the experts have received several documents and samples and have conducted many interviews," the UN said in a statement.

The UN team's first report, issued on September 16, said there was evidence that sarin had been used in the August 21 attack.

But the experts are mandated only to investigate whether chemical weapons were used, not to determine who was responsible for their use.

Both the Syrian regime and the rebels seeking its overthrow have repeatedly accused each other of using chemical weapons.

But in the wake of the August 21 attack, which allegedly left hundreds dead, the United States threatened military action against the Syrian regime, which it accuses of responsibility.

The regime denies involvement but agreed soon afterwards to relinquish its chemical arsenal under a US-Russian deal, which was enshrined in a landmark UN Security Council resolution on Friday.