An envoy said authorities traveled to Syria to address inconsistencies between an initial rundown of its chemical arms and removed stocks, Reuters reports.
The Western official said enforcers of an international chemical-arms ban began the visit last week, days before their agency announced it would look into claims that combatants have employed chlorine gas in the nation's 3-year-old civil war.
Syrian President Bashar Assad's government filed additional details earlier this month on the chemical-warfare inventory it reported last year to the Organization for the Prohibition for Chemical Weapons. The regime agreed to relinquish the materials last year, after sarin nerve gas killed hundreds of people on the edge of the Syrian capital and bolstered discussion of a possible foreign military intervention.
The anti-Assad Syrian National Coalition on Tuesday urged OPCW investigators to look for undeclared regime chemical arms, in addition to examining the chlorine claims.
The coalition noted Western intelligence indications that Assad may be concealing warfare chemicals from international authorities. Inspectors should visit sites operated by the Syrian Scientific Studies and Research Center, the rebel group added in an e-mailed statement.
An independent study by the London Telegraph links Assad's regime to the alleged chlorine strikes, the newspaper reported on Tuesday. The government is not required to surrender any chlorine under an international chemical-arms treaty it joined last year, though the pact prohibits use of the toxic industrial material as a weapon.
Damascus has consistently blamed chemical attacks on its opponents.
Russia, an ally of Assad, on Wednesday affirmed the regime's assertion that an alleged April chlorine attack in the town of Kfar Zeita was the work of the al-Nusra Front, al-Qaida-affiliated opposition group, ITAR-Tass reported.
"We expect that unbiased work of international experts will make it possible to find out what really happened and will expose those responsible," the Russian foreign ministry stated.