Inspectors have been indefinitely blocked from entering the Damascus suburb of Douma, the site of the Syria regime’s chemical attacks on April 7, after a UN team came under gunfire on Tuesday.

The Organization for the Prohibition of Chemical Weapons confirmed on Wednesday that the inspection, already held up by the Assad regime, will be suspended.

The UN security team had entered Douma to inspect the sites struck by two chemical attacks to force a surrender agreement in the last opposition-held area near the Syrian capital. They came under small arms fire, and had to withdraw from the first site. when confronted by a large crowd. An explosive device was detonated nearby during their stop at the second site.

No attacker was identified, but the incident is likely to give the regime — which had citing “security issues” to keep the OPCW group in Damascus since Saturday — the pretext to continue the delay of any inspections.

“The UNDSS [security team] will continue to work with the Syrian National Authority, the local Councils in Douma, and the Russian Military Police to review the security situation. At present, we do not know when the [Fact-Finding Mission] team can be deployed to Douma,” a statement said.

Russia has already vetoed any inspection which can formally attribute responsibility for the chemical attacks, reportedly carried out by Assad regime helicopters, and Russian personnel have removed or disturbed evidence from the site, according to multiple sources.

Ishak Majali, a former OPCW inspector, said it is unlikely inspectors will now be able to collect evidence from the sites:

It has been a lot of time since the attack took place – we are talking about 11 days.

So, if you are in control of a site with chemicals for such a long time, it’s very easy actually to tamper with the place and to change the facts on the ground.

You can actually do what we call it in the military business as the decontamination process, which is to remove all the evidence on the ground by using other chemicals to neutralise the chemicals on the ground. Also, you can tamper with the munition itself … to prepare some witnesses or to prepare some medical reports.