By (AP) Beirut – Assailants opened fire at a UN security team visiting the site of a suspected chemical weapons attack in Syria, an official said Wednesday, forcing it to retreat to its base and further delaying a fact-finding mission by outside experts to examine the claims. Gunmen shot at the UN team in Douma on Tuesday and detonated an explosive, leading it to return to Damascus, said the head of the international chemical weapons watchdog, Ahmet Uzumcu. He did not identify the assailants. Inspectors from the Organization for the Prohibition of Chemical Weapons have been waiting since Saturday to visit Douma, the site of the alleged April 7 attack. They were initially blocked by the Syrian government and its ally, Russia, on Monday. Then on Tuesday, the advance security team from the UN came under fire, compounding the delays. The OPCW inspectors have not yet been able to visit the site, and Uzumcu did not say when they would deploy. The United Nations said more security measures were needed before the inspectors could go in. "There is still a lot of volatility in the area," UN spokesman Stephane Dujarric said, adding that the UN security team needed to make at least another visit before the fact-finding mission could go ahead. The town is under the protection of Russia's military police. The Russian military said a Syrian security employee was slightly wounded in the crossfire Tuesday, but no Russian servicemen were at the site of the attack. Journalists visiting Douma on a government-organized tour Monday did not report any security threats. The Associated Press met with residents who said they were overwhelmed by chlorine fumes on the night of the alleged attack, and lost their loved ones.