A bipartisan group of US senators introduced a bill on Thursday aimed at penalising Moscow for alleged meddling in US elections and its activities in Syria and Ukraine.

It includes restrictions on new Russian sovereign debt transactions, energy and oil projects and uranium imports, and new sanctions on politicians and oligarchs.

The rouble fell as low as 63.55 per dollar, its lowest since July 20, after the bill was announced.

It was little changed on Friday, dipping 0.1 percent to 63.48 by 0944 GMT and also down 0.1 percent at 73.50 versus the euro.

It gained some support from Brent crude oil, a global benchmark for Russia's main export, which rose 0.16 percent to $73.57 a barrel.

Artyom Zvonaryov, an analyst with VTB Capital, said speculative sales of hard currency were also underpinning the rouble.

That factor was offset, however, with news that the Finance Ministry would increase daily purchases of foreign currency for state reserves to the equivalent of 16.7 billion roubles ($263.4 million) between Aug. 7 and Sept. 6.

BCS analysts said they expected the rouble to remain under pressure.

"The (new) US bill will continue to pressure the markets, although the possibility of its approval by the US Congress in this form is not high," analysts at BCS brokerage said in a note.

Russian stock indexes were mixed. The dollar-denominated RTS index was down 0.03 percent at 1,140 points and the rouble-based MOEX Russian index was up 0.09 percent at 2,297 points.