WASHINGTON (AP) — The struggling U.S. Postal Service on Thursday reported an annual loss of a record $15.9 billion and forecast more red ink in 2013, capping a tumultuous year in which it was forced to default on billions in payments to avert bankruptcy.

The financial losses for the fiscal year ending Sept. 30 were more than triple the $5.1 billion loss in the previous year. Having reached its borrowing limit, the mail agency is operating with little cash on hand, putting it at risk in the event of an unexpectedly large downturn in the economy.

"It's critical that Congress do its part and pass comprehensive legislation before they adjourn this year to move the Postal Service further down the path toward financial health," said Postmaster General Patrick Donahoe, calling the situation "our own postal fiscal cliff."