India's central bank unexpectedly raised its key interest rate, signaling it's ready to implement the most sweeping changes in its 78-year history to fight the fastest consumer-price gains in Asia.

Governor Raghuram Rajan boosted the repurchase rate to 8 percent from 7.75 percent, the Reserve Bank of India (RBI) said today. Only three of 45 analysts in a Bloomberg News survey predicted the move, with the rest expecting no change. It came five days after Finance Minister Palaniappan Chidambaram offered a reminder that the central bank has a duty to help growth.

"The gravest risk to the value of the rupee is from CPI [consumer price index] inflation, which remains elevated close to double digits," Rajan said in a statement. "It's only by bringing down inflation to a low and stable level that monetary policy can contribute to reviving consumption and investment in a sustainable way."