MOSCOW Russia's central bank will hold an extraordinary meeting on Tuesday to discuss the level of its key interest rate, it said on Monday, as the sharply weakening rouble prompted calls for higher borrowing costs.

President Vladimir Putin's economic adviser rebuked the central bank on Monday as the rouble slid past 101 per U.S. dollar, blaming loose monetary policy in a sign of growing discord among Russia's monetary authorities.

The bank, whose key rate is currently 8.5%, had been scheduled to hold its next meeting on rates on Sept. 15. The bank said it would announce the board's decision at 10:30 Moscow time (0730 GMT).

The rouble pared its losses and firmed back to below 100 per U.S. dollar after the central bank announced Tuesday's meeting.

(Reporting by Reuters; Writing by Alexander Marrow; Editing by Gareth Jones)