Russia's central bank may raise its key rate to an average of 12.5-13.5% next year from the current 8.5% if substantial risks materialise, it said in a monetary policy presentation on Friday, outlining possible scenarios.

The bank's baseline scenario, unchanged since last month, puts the average interest rate at 8.5-9.3% this year and 8.5-9.5% next year.

The bank also has a "greater fragmentation" scenario which includes stronger Western sanctions against Moscow that would require greater monetary tightening, it said.

The bank said there was a risk that sanctions and declining global energy prices could drive down Russia's oil and gas revenue to an extent that even the rouble's moderate weakening would not be sufficient to offset.

That, in turn, would undermine Russia's budget rule which aims to maintain a liquidity cushion in the "rainy-day" National Welfare Fund. (Reporting by Elena Fabrichnaya Writing by Olzhas Auyezov Editing by Gareth Jones)