The central bank will start buying FX for the finance ministry's reserves from Jan. 15, restoring daily downside pressure on the rouble that eased in late August when it suspended FX buying amid increased market volatility.

The finance ministry is set to report the FX purchasing plan at 0900 GMT. A Reuters poll showed the central bank is expected to buy 280 billion roubles ($4.2 billion) worth of currencies on behalf of the finance ministry by Feb. 6.

At 0801 GMT, the rouble was unchanged at 66.93 versus the dollar and had eased 0.3 percent to trade at 77.15 versus the euro.

While the resumption of state FX buying was cited by market players as a clear factor behind the rouble weakness in the past few days, financial authorities played down such concerns.

Alexei Zabotkin, head of the central bank's monetary policy department, said the market had already priced in the resumption of foreign exchange purchases, so these operations should not change the market balance.

The resumption of state FX buying will limit the room for rouble strengthening in the future, but its impact will be partially offset by Russia's current account surplus, analysts at Rosbank said in a note.

Russian stock indexes rose on Friday as oil prices were on track for solid weekly gains. Brent crude oil, a global benchmark for Russia's main export, was up 0.1 percent at $61.73 a barrel.

The dollar-denominated RTS index was up 0.3 percent to 1,146.27 points. The rouble-based MOEX Russian index was 0.1 percent higher at 2,436.18 points.