At 0708 GMT, the rouble was 0.23 percent weaker against the dollar at 57.84 and had lost 0.16 percent to trade at 70.74 versus the euro.

Sources familiar with the matter told Reuters on Wednesday the United States plans to sanction Russian oligarchs this week under a law targeting Russia for its alleged meddling in the 2016 US election.

The Kremlin has said it will wait to see what penalties are imposed by Washington before reacting, but fresh sanctions will further sour fraught relations between Moscow and the West.

Lower prices for oil, Russia's main export, and the finance ministry's plans to buy more FX this month also played to the rouble's downside.

Benchmark Brent crude oil was down 0.56 percent at $67.95 a barrel after US President Donald Trump's threat of new tariffs on China reignited fears of a trade war between the world's two biggest economies.

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

Russian stock indexes were down.

The dollar-denominated RTS index was down 0.58 percent to 1,246.07 points. The rouble-based MOEX Russian index was 0.4 percent lower at 2,287.10 points.