UN officials and a global watchdog on Friday criticized incomplete declarations from Syria on chemical weapons while its ally Russia sought to push back against the accusations.

During a videoconference at the UN Security Council, officials from the United Nations and the Organization for the Prohibition of Chemical Weapons (OPCW) said Syria had failed to respond to a series of 19 questions involving toxic arms.

Izumi Nakamitsu, UN high representative for disarmament affairs, said the OPCW had found that because of unresolved gaps and discrepancies Syria's declarations "cannot be considered accurate and complete in accordance with the Chemical Weapons Convention."

OPCW Director-General Fernando Arias said one of the questions involved a chemical weapons production facility declared by Syria as never having been used for chemical weapons production.

Information and material gathered since 2014 indicates the facility was used for "production and/or weaponization of chemical warfare nerve agents," he said, without specifying the location.

OPCW investigators have accused President Bashar al-Assad's regime of sarin gas and chlorine attacks in Syria in 2017.

Russia and Syria have dismissed the charges, saying Western powers have politicized the work of the OPCW.

"What we reject is speculations and political smear campaigns, which, unfortunately, more and more often poison the OPCW," said Russia's ambassador to the United Nations, Vasily Nebenzya.

A man tries on an air permeable charcoal impregnated suit during a simulation at OPCW headquarters in The Hague, The Netherlands, on April 20, 2017
A man tries on an air permeable charcoal impregnated suit during a simulation at OPCW headquarters in The Hague, The Netherlands, on April 20, 2017 AFP / JOHN THYS

He alleged the organization was relying on remote investigations instead of on-site collections of samples.

In a joint statement ahead of the meeting, European members of the Security Council expressed their full backing for the OPCW.

Germany, Belgium, Estonia, France and Britain praised "its professionalism, impartiality and well-established technical expertise in implementing the Chemical Weapons Convention and tasks assigned by the states parties."

The United States also said it "strongly" supported the global watchdog.

Russia and Syria have been under pressure for months by the UN and the OPCW to provide clarification on chemical attacks carried out in Syria and poisonings of Russian nationals.

Although the meeting was devoted to chemical weapons in Syria, Arias spoke at length on the case of Russian opposition leader Alexei Navalny, who says he was poisoned by the Kremlin.

He particularly regretted that Moscow is still blocking a technical visit by the OPCW to Russia.

The OPCW has said samples taken from Navalny have contained a Novichok-type nerve agent.