(Reuters) - Inspectors have not yet been granted access to sites in Douma, Syria, the British delegation to the Organization for the Prohibition for Chemical weapons said on Monday, citing the agency’s director general.

The inspectors arrived on Saturday to examine whether chemical weapons were used at Douma on April 7, and if so what kind.

The British delegation to the OPCW said in a statement posted on Twitter that Russia and Syria had not yet allowed inspectors access to Douma.

“Unfettered access (is) essential” the statement said. “Russia and Syria must cooperate.”

Russia’s deputy foreign minister said the delay was due to U.S. air strikes.