An international chemical weapons monitor group said a team of inspectors collected samples Saturday at the site of an alleged gas attack two weeks ago in the Syrian town of Douma.
The Organization for the Prohibition of Chemical Weapons said a report based on the findings and other information gathered by the team will be drafted after the samples are analyzed by designated laboratories.
The group added it will "evaluate the situation and consider future steps, including another possible visit to Douma."
The fact-finding team's attempts to enter the town were postponed several days due to a series of security-related setbacks.
Emergency responders said at least 40 people were killed in the suspected April 7 gas attack, which the U.S. and its allies blamed on the regime of Syrian President Bashar al-Assad.
The Syrian government has denied using chemical weapons, a violation of international law, and invited the inspectors to investigate.
They arrived in Syria on April 14, the same day the United States, Britain and France launched a barrage of missiles targeting three chemical weapons facilities in Syria.
Ken Ward, the U.S. ambassador to the OPCW, claimed on April 16 the Russians had already visited the site and "may have tampered with it," a charge Moscow rejected.
On April 9, Moscow's U.N. ambassador told the U.N. Security Council that Russian experts had visited the site, collected soil samples, interviewed witnesses and medical personnel, and determined no chemical weapons attack had taken place.
U.S. military officials have said the air strikes were designed to send a powerful message to Syria and its backers, showing that the United States, Britain and France could slice through the nation's air defense systems at will.