A UN security team was fired at while on a reconnaissance mission in the Syrian town of Douma ahead of the deployment of experts investigating an alleged chemical attack, according to a UN official.
The forward team had been assessing the security situation when they came under fire, though none were injured.
Peter Wilson, Britain’s ambassador to the UN, told reporters in The Hague that the security team on Tuesday travelled to two sites in Douma, escorted by Russian security police.
The officials were greeted by a “large crowd” of protesters at one site, forcing them to withdraw while at the second site “they were subject to small-arms fire and an explosion,” Mr Wilson said.
The Organisation for the Prevention of Chemical Weapons (OPCW) inspectors arrived in Syria on Saturday, but have so far been unable to reach the site of the April 7 attack to carry out tests.
They said they did not know who was responsible.
Jaish al-Islam, the rebel group which had been in control of Douma, agreed to leave the town in an evacuation deal agreed with Russia the day after the attack.
Under the terms of the deal Douma was to be emptied of heavy and medium weaponry, but those who stayed behind were allowed to keep light arms.
Thousands of its fighters were sent to opposition-held areas near the Turkish border in the days after and Russia declared it was in “full control” of the enclave on April 12.
The OPCW team will seek evidence from soil samples, interviews with witnesses, blood, urine or tissue samples from victims and weapon parts. But, more than a week after the suspected attack, hard evidence might be hard to trace.
The US, UK and France say that, based on open source information and their own intelligence, they are confident chlorine and possibly a nerve agent were used.
They launched a joint missiles strike on chemical facilities near Damascus and the central city of Homs on Saturday morning.
The US has expressed concerns that the delay may have given the Russian troops in control of the area the time to interfere with evidence.
“It is our understanding the Russians may have visited the attack site. We are concerned they may have tampered with it with the intent of thwarting the efforts of the OPCW fact-finding mission to conduct an effective investigation,” Kenneth Ward, US ambassador to the OPCW, said in comments at a closed-door meeting in The Hague that were later made public.
France’s foreign ministry also said in a statement that it was “very likely that proof and essential elements are disappearing from this site”.
While the inspectors have been denied access, a small group of journalists was allowed to report from the scene of the attack earlier this week.
The Associated Press spoke to survivors, who said they encountered a powerful smell like chlorine. CBS News broadcast footage of what experts said appeared to be chlorine canisters.
Some residents told pro-government al-Ekhbariya television channel that the dust had triggered an asthma attack and had not been the effect of poisonous gas.
Activists from Douma who have been displaced and now living under rebel areas elsewhere in the country suggested that they spoke under duress and that those who stayed were coerced into making the statements in return for being allowed to remain in their homes.
Civil defence rescuers, known as the “White Helmets”, revealed on Wednesday that the victims of the April 7 chemical strike have been hidden in a secret location, which has been shared only with the OPCW.