U.S. Defence Secretary Chuck Hagel will announce later today that most of the Defence Department's 800,000 civilian employees will be placed on unpaid leave for 11 days, as the military scrambles to comply with budget cutting targets by the end of September.

Hagel will announce the decision at a town hall meeting with Defence Department employees.

The furlough is shorter than the earlier estimates of 14 days issued in March and 22 days in February, but is still going to be deeply unpopular among the Pentagon workforce.

"He made this decision after carefully studying all of the options," said one U.S. defence official, adding that Hagel was not happy about the move but that it was necessary to meet budget cutting targets.

A second U.S. defence official, also speaking on condition of anonymity, said more than 600,000 employees would go on unpaid leave but could not offer a precise figure. They would not start their leave for several weeks, the official added.

Defence spending has taken the single biggest hit from automatic spending cuts, known in Washington-speak as the "sequester," with a $46 billion reduction through the Sept. 30 end of the current fiscal year.

The cuts were included in a 2011 law aimed at reducing the federal government's yawning deficits and controlling the national debt.

But top brass have warned Congress that the cuts will erode military readiness to respond in the future to global tensions, including over the civil war in Syria, and as the United States winds down the 11-year-old war in Afghanistan.