The U.S. State Department says Russia has tried to block an international watchdog from investigating a suspected chemical attack in Syria "by making it more complicated" for the specialists to do their work.
"They probably want to do that because they recognize that the longer that a site goes untested the more that the elements, the chemicals, can start to disappear," State Department spokeswoman Heather Nauert told Alhurra television.
The investigators from the Organization for the Prohibition of Chemical Weapons arrived in Syria on Saturday, but so far have not been able to begin their work in Douma.
A Russian official says the OPCW team is set to visit the area east of Syria's capital on Wednesday.
Russia has blamed the delays on airstrikes carried out Saturday by the United States, France and Britain on three Syrian chemical weapons facilities. Russia's Deputy Foreign Minister Sergei Ryabkov also said the mission was not allowed in because it lacked approval from the United Nation’s Department for Safety and Security.
U.N. officials in New York disputed the claim.
"The United Nations has provided the necessary clearances for the OPCW team to go about its work in Douma," said U.N. spokesman Stephane Dujarric. "We have not denied the team any request for it to go to Douma."
He added that U.N. Secretary-General António Guterres is very supportive of the investigation.
"The secretary-general wants to see the fact-finding mission have access to all the sites it needs to have access to, so that we can have the most thorough and full picture of the facts," Dujarric said.
The U.S. envoy to the OPCW, Ken Ward, said Monday it was his understanding Russia had already visited the site and he raised concerns of tampering before the OPCW carries out its fact-finding mission.
Russian Foreign Minister Sergey Lavrov denied that accusation, telling the BBC he guarantees Russia "has not tampered with the site."
Lavrov said that evidence cited by the United States, Britain and France to justify Saturday's missile attack was based "on media reports and social media." He denied any chemical weapons attack had occurred, accusing Britain of staging the attack.
The Group of Seven leading industrialized nations issued a joint statement Tuesday endorsing the airstrikes.
"We fully support efforts made by the United States, the U.K. and France to decrease the capacity to use chemical weapons by the Assad regime and to prevent their future use," the leaders of Canada, France, Germany, Italy, Japan, Britain, the United States and European Union said.
Syrian media reported another missile attack early Thursday in Homs province, but later said it was a false alarm and not an outside attack that triggered air defense systems.
Syrian media reported another missile attack early Thursday in Homs province, saying government air defenses shot down most of the missiles fired at an air base. The reports did not say who was responsible, and the U.S. military said neither it nor the coalition it leads was operating in that area at the time.
Nauert told Alhurra the United States is pushing for a renewed focus on the so-called Geneva process the United Nations began in 2012 as a roadmap for ending the Syrian conflict with a new constitution and elections.
"The only thing that I can hope that is positive that came out of the terrible news in Syria last week is to reinvigorate that political process," she said. "So it is our hope now that countries will go back to the Geneva process and we’ll be able to make some progress there."
EU foreign policy chief Federica Mogherini made a similar call Monday ahead of a ministerial meeting, saying there is a clear need to push for re-launching the U.N.-led peace process.
Margaret Besheer contributed to this report.