The international monitoring group investigating a suspected chemical weapons attack on a Syrian town said its experts had finally been able to visit the site on Saturday after repeated delays and they collected samples for analysis.

The Organization for the Prohibition of Chemical Weapons said its experts had reached the Damascus suburb of Douma a week after they arrived in Syria.

“The O.P.C.W. will evaluate the situation and consider future steps including another possible visit to Douma,” the organization said, adding that its experts had taken “samples for analysis in connection with allegations of chemical weapons.”

Western nations have accused President Bashar al-Assad of Syria of an April 7 chemical weapons attack on Douma that killed 43 people. The United States, Britain and France carried out airstrikes a week later on military targets to punish Mr. Assad for what they called his repeated violations of the treaty banning chemical weapons.