If the ceiling is not raised, the United States would only have weeks before it runs out of cash to pay its bills, according to government estimates.
The Treasury had expected to run up against the ceiling between April 5 and May 31.
The warning came as US lawmakers, battling over how to slash spending, eyed a stopgap measure to avert a government shutdown.
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Although the issues of extending the debt ceiling and keeping the government funded are not linked, they have become enmeshed thanks to Washington’s political deal making.
President Barack Obama’s Republican foes have tied raising the debt limit to fierce spending cuts, which are seen as too extreme by many Democrats.