The US Treasury says the government shutdown does not affect its position and it will still run out of funds on October 17 without a debt ceiling hike.
Treasury Secretary Jacob Lew told House of Representatives Speaker John Boehner in a letter that the partial shutdown of the government, which began on Tuesday due to lack of a budget, would not materially change the projections he made last week for when the Treasury would hit its limit.
Although the lack of a budget for the new fiscal year "creates some additional uncertainty", it would not change the Treasury's position unless the impasse continues "for an extended time".
Lew warned again that not increasing the debt ceiling by October 17 would force the US government to default on its obligations - though he did not specify which of those obligations it would likely fail to pay.
"Not later that October 17," he said, "we will be left to meet our country's commitments at that time with only $US30 billion ($A32 billion)."
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"This amount would be far short of net expenditures on certain days, which can be as high as $US60 billion ($A64 billion)," he added.
Congressional Republicans have refused both to pass a budget for the fiscal year which began on Tuesday, and to raise the $US16.7 trillion ($A17.8 trillion) debt ceiling, as they push for political and fiscal concessions.
The country is running a deficit of about $US60 billion ($A64 billion) a month and needs to raise that much from lenders to finance its deficit.
The Treasury has been able to operate just under the ceiling since May using "extraordinary measures" to adjust its accounts and continue to pay the country's bills, from salaries and pensions to servicing debt.
But Lew says those measures have been exhausted, and new borrowing will be required by October 17, or some bills - or the debt - will go unpaid.
