The agency responsible for safeguarding the US nuclear stockpile began placing most staff on enforced leave Monday, an official said, as yet another congressional vote to end the crippling government shutdown failed.

With the standoff about to enter its fourth week, some 1,400 workers at the National Nuclear Security Administration were due to receive notices telling them they had been placed on unpaid furlough.

"Due to the Democrat shutdown, approximately 1,400 NNSA federal employees will be furloughed as of today, October 20th and nearly 400 NNSA federal employees will continue to work to support the protection of property and the safety of human life," a Department of Energy spokesperson said in a statement.

The United States has an arsenal of 5,177 nuclear warheads, with about 1,770

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