NIGERIA'S central bank has barred commercial lenders from accepting foreign currency-denominated collateral to grant naira loans, a move that could protect the banking system against a strengthening of the local currency, it said on Monday. The regulator said in a circular that the practice it had observed of bank customers using foreign currency as collateral for naira loans was "prohibited". The central bank on Monday said it approved Eurobonds issued by the government or letters of credit issued by an offshore bank as eligible foreign currency collateral. It told lenders to wind down all loans currently secured with dollar-denominated collateral…