LUSAKA, Oct 31 (Reuters) - Zambia's central bank increased its benchmark interest rate by 25 basis points to 9.25 percent on Wednesday, saying its monetary policy committee had noted upward risks to inflation. "The committee weighed the risks and was of the opinion that inflationary pressures during the policy-relevant period may pose a threat to the end-year inflation target of 7.0 percent," it said in astatement.