US President Donald Trump's administration dramatically raised the stakes Thursday in a clash over a possible government funding shutdown, telling federal agencies to prepare for new mass firings if it goes ahead.

The White House Office of Management and Budget (OMB) warned in a memo that it would go beyond the usual practice of temporary furloughs during previous shutdowns, where Congress cannot agree on spending plans.

Republican Trump is in a tense showdown with congressional Democrats over federal funding ahead of a fiscal deadline of midnight on September 30, which would trigger a fresh political crisis in Washington.

Democrats have rejected Republican proposals, unless some of the spending cuts are reversed and existing health care subsidies are extended.

Trump blamed Democrats f

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