Republicans have insisted they were no closer to a deal with Democrats to end the shutdown of US federal services despite forward movement.

Defence Secretary Chuck Hagel issued a "back to work" command to civilian workers at the Pentagon on Saturday.

The House of Representatives also agreed that staff locked out by the impasse in Washington could receive back-pay once the shutdown ends.

Mr Hagel said his order was based on the old Pay Our Military Act, designed to stop the immense US war machine from grinding to a halt alongside other public services when Washington fails to pass a budget.

The law does not allow for the return of all the Pentagon's 350,000 civilian employees but for those whose responsibilities "contribute to the morale, well-being, capabilities and readiness of service members."

The shutdown started six days ago, when House Republicans refused to pass the budget unless Democrats agreed to sabotage limited health care reforms known as "Obamacare" which have already passed into law.

It has seen over 800,000 public-sector workers sent home and national parks, zoos, museums and other state-run services shut.

Democrats said Saturday's agreement to pay staff later should lead to an agreement to allow all federal employees to return to work, but Republican House Speaker John Boehner said no solution was yet on the cards.

If the US fails to pass the budget and raise its borrowing ceiling by October 17 the nation will default on its debts for the first time in its history.