A United Nations security team doing reconnaissance in Syria’s Douma, the site of a chemical weapons attack, came under fire a day earlier, said the Organization for the Prohibition of Chemical Weapons on Wednesday. OPCW Director General Ahmet Üzümcü told a meeting at the organizations headquarters in The Hague that the security team was forced to withdraw, delaying the arrival of chemical weapons inspectors due to visit the site. Sources present at the closed-door meeting briefed Reuters on Üzümcüs remarks. At least 40 people were killed in the April 7 attack on Douma that prompted an air strike by the United States, Britain and France against Syrian regime chemical facilities. A delay in the arrival of the inspectors at the Douma site has become a source of diplomatic dispute, because Western countries accuse Damascus and Moscow of hindering the mission. The United States and France have both said they believe the delay could be used to destroy evidence of the poison attack. Several experts have said any investigation at this stage was likely to be inconclusive. "As with any crime scene, it is crucial to get there as soon as possible," said Olivier Lepick, a fellow at the Paris-based Foundation for Scientific Research. "If the Russians and Syrians have nothing to hide, its strange that they would wait 36 to 72 hours," he said. "Its probably to give themselves the time to finish cleaning up." Russia and Syria deny using poison gas, hindering the investigation or tampering with evidence. One source told Reuters the advance team had "encountered a security issue" during the visit to Douma, including gunfire which led to the delay. The source could not provide additional details. A UN source said the OPCW inspectors would probably not be going to Douma on Wednesday. The source did not give details of the shooting incident. The source did not say when the inspectors might visit the site, or whether a planned visit to Douma on Wednesday had been postponed.