Unidentified snipers shot at and damaged a vehicle being used by U.N. chemical weapons investigators in Damascus today as they sought to reach the site of a suspected poison gas attack, a U.N. spokesman said.

"The first vehicle of the Chemical Weapons Investigation Team was deliberately shot at multiple times by unidentified snipers in the buffer zone area," the spokesman said, adding the car was no longer serviceable and a replacement vehicle was being obtained.

The spokesman added: "It has to be stressed again that all sides need to extend their cooperation so that the team can safely carry out their important work."

The team was trying to visit one of the sites of an Aug 21. attack in which, doctors and opposition activists say, suspected nerve agents killed hundreds of civilians in several outlying districts of the Syrian capital.

The U.N. investigation comes amid rising calls by Western powers for reprisals against President Bashar al-Assad's government, who they say was responsible for the attack.

Syria agreed on Sunday to allow the inspectors to visit the sites. But the United States and its allies say evidence has probably been destroyed by heavy government shelling of the area over the past five days.