The U.S. Postal Service says it lost $5.1 billion last year as a weak economy and increased Internet use drove down mail volume.

The bleak financial report for the fiscal year ending Sept. 30 was not as high as the $10 billion in losses previously estimated. But that's because an annual payment of $5.5 billion the post office owed the federal government has been deferred to a later date.

Postal officials called the financial situation "dire." They say the Postal Service will not be able to make the $5.5 billion payment due this Friday due to low cash flow.

Postmaster General Patrick Donahoe has warned of a postal shutdown next year unless there is congressional action to address the agency's long-term money problems.