A team from the Organisation for the Prohibition of Chemical Weapons -- OPCW -- visited a site in Douma, Syria, on Saturday "to collect samples for analysis" in connection with an alleged chemical weapons attack that prompted a retaliatory missile strike by the U.S., U.K. and France last weekend.

The OPCW announced the visit in a statement, saying it "will evaluate the situation and consider future steps including another possible visit to Douma."

Inspectors from OPCW has been delayed for a week in Damascus before they could visit the town -- just minutes' away from the capital -- where the alleged attack occurred on April 7. Security concerns had been keeping international experts from inspecting the site, CBS News' Seth Doane reported. An advance security team from the United Nations withdrew from Douma after coming under small arms fire on Tuesday at one of the sites destined for inspection. There was also a small explosion at the site. That further delayed the international weapons inspectors, who arrived in Damascus last weekend to try to determine what happened in early April.

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Russian ministry spokeswoman Maria Zakharova said Saturday in a statement that the delays to the OPCW team were "unacceptable."

The town of Douma was, at the time of the attack, under rebel control and facing a ferocious government air and ground assault. Militants gave up the town days after the alleged attack, which killed more than 40 people.

The U.S., France, and Britain blamed the Syrian government, and struck suspected Syrian chemical weapons facilities one week later. The Syrian government and its ally Russia have denied responsibility for the attack.

Images that emerged from Douma in the hours after the attack showed lifeless bodies collapsed in crowded rooms, some with foam around their noses and mouths. Thousands of people -- rebels and civilians -- left Douma on buses to north Syria in the days afterward, believing they could not reconcile with the government after it took over the town. North Syria is divided between opposition, Turkish, and al-Qaida control.

The evacuations were the latest in a string of population transfers around the Syrian capital that have displaced more than 60,000 people as the government reconsolidates control after seven years of civil war.

U.N. officials and human rights groups say the evacuations amount to a forced population displacement that may be a war crime.

On Saturday, rebels began evacuating three towns in the eastern Qalamoun region in the Damascus countryside, state TV reported. State-run Al-Ikhbariya TV said several buses left the towns of Ruhaiba, Jayroud, and al-Nasriya carrying hundreds of rebels and their families to opposition territory in north Syria.

The station said there could be 3,200 rebels leaving three towns on Saturday. It said the evacuations will continue for three days.

Syrian government forces will take over the towns once the departures are complete.