By 0939 GMT, the rouble was 0.3% weaker against the dollar at 73.73 RUBUTSTN=MCX, after touching a more than one-week high of 73.3750 in early trade.
It had lost 0.1% to trade at 89.87 versus the euro EURRUBTN=MCX.
A Reuters survey of analysts had forecast a drop in regular FX sales to around 15 billion roubles for the month ahead, but not the switch to purchases.
Sofya Donets, chief economist at Renaissance Capital, told Reuters the volume of purchases was higher than expected and marked a significant change.
"However, the increase in global oil prices we are seeing above $55 should cushion this transition and support the rouble," she added.
Brent crude oil LCOc1, a global benchmark for Russia's main export, was up 0.6% at $56.90 a barrel, earlier reaching its highest since February last year, and sending shares of the Russian oil companies, namely Rosneft ROSN.MM and Lukoil LKOH.MM, higher.
Later on Wednesday, the finance ministry will offer two OFZ bonds at auction. These bonds are popular among foreign investors for their lucrative yields.
Externally, global optimism for economic recovery was fuelled by expectations of a large stimulus package from the United States, said BCS Global Markets in a note, but increasing COVID-19 cases were weighing on sentiment.
Russian stock indexes were climbing.
The dollar-denominated RTS index .IRTS was up 0.1% to 1,486.4 points. The rouble-based MOEX Russian index .IMOEX was 0.2% higher at 3,478.0 points, just shy of an all-time high.
For Russian equities guide see RU/EQUITY
For Russian treasury bonds see 0#RUTSY=MM
(Reporting by Alexander Marrow, additional reporting by Elena Fabrichnaya; editing by Barbara Lewis)
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