The Obama administration warned on Monday it could start defaulting on the government's obligations "very soon" after it runs out of room to borrow under a legal cap on public debt.
Washington is due to reinstate a limit on its borrowing at the end of this week and Treasury Secretary Jack Lew said the administration can use accounting measures to stay under the new cap until the end of February.
(Read more: Lew warns Congress of February debt ceiling deadline)
After that time, "very soon it would not be possible to meet all of the obligations of the federal government," Lew said at an event hosted by the Bipartisan Policy Center, a prominent Washington think tank.
U.S. politicians now partake in a regular dance around the country's so-called debt limit. First, Congress authorizes spending that outstrips tax receipts. Then lawmakers balk over whether to OK enough borrowing to pay the bills. A rancorous debate ensues over putting public finances on a stable path.