U.S. lender Bank of America says it is owed $160 million on unpaid insurance claims made on failed mortgages, court papers say.

In a lawsuit filed in Charlotte, N.C., the banking giant says Old Republic Insurance Co. has denied "thousands" of valid claims and is making excuses not to cover them.

The lawsuit says from 2009 to 2010 claims honored by Old Republic fell 75 percent. Old Republic, in turn, said it was turning down claims with inadequate paperwork, The Charlotte Observer reported Thursday.

With Bank of America already caught in a controversial review of foreclosures brought on by numerous court challenges over flawed documents, "This is just another phase of the crisis," said Keith Gumbinger, vice president of mortgage analysis at HSH Associates.

Bank of America said faulty paperwork has "nothing to do" with the reason Old Republic is failing to honor mortgages it insures.

BofA says it continues to pay Old Republic's premium of $870,000 each month to cover "a percentage" of its loans.