At 1013 GMT, the rouble was 0.6 percent weaker against the dollar at 57.88, its weakest since March 28, and eased 0.6 percent to 71.09 versus the euro.

The finance ministry, which started buying foreign currency for its reserves in February 2017, said it would buy 25 percent more dollars and other currencies in April than in March.

That would drive the rouble towards 59.6 against the dollar in the second quarter, analysts at Rosbank, a subsidiary of Societe Generale, said in a note.

Brent crude futures dropping 1.8 percent to $66.90 pushed the dollar-denominated RTS index down 0.9 percent to 1,225.6 points, while rouble-based peer MOEX dropped 0.5 percent to 2,252.8 points.

The Organisation for the Prohibition of Chemical Weapons (OPCW) holds a special session on the poisoning of former double agent Sergei Skripal in March, which plunged relations with the West into the worst crisis since the Cold War.

Russia's President Vladimir Putin said he hoped would help to defuse the diplomatic row but the British OPCW delegation dismissed a Russian proposal for a joint U.K.-Russian investigation as "perverse".