US Vice-President JD Vance has warned of further workforce cuts in addition to the thousands of jobs already axed if the government shutdown is not resolved.

"The longer this goes on, the deeper the cuts are going to be," Vance told Fox News. "To be clear, some of these cuts are going to be painful."

Democrats said Republicans were punishing people by refusing to attach health insurance subsidies to the spending bill.

Hundreds of thousands of federal employees are already on leave without pay as the shutdown approaches its third week. No congressional vote is scheduled that could reopen the government.

The standoff began on 1 October after Democrats rejected a short-term funding bill. They want the budget to include an extension of federal subsidies for health insurance under the Affordable Care Act.

The Trump administration announced on Friday that seven agencies, including the CDC, had started firing over 4,000 staff.

But some of those CDC layoff notices were sent in error, a spokesman for the US health department, which oversees the CDC, told the BBC.

Those CDC employees "have all been notified that they are not subject to the reduction in force", Andrew Nixon said.

Out of about 1,300 CDC workers who were fired on Friday, around 700 were reinstated on Saturday, the employees' union told CNN.

Essential workers like federal law enforcement officers and air traffic controllers are required to continue working without pay.

But the Trump administration is making an exception for some essential workers: US service members.

Trump directed Secretary of War Pete Hegseth to find available funds to get troops their wages this week - and Hegseth delivered.

The Department of Defence is taking about $8bn (£6bn) from "unobligated research development testing and evaluation funds" to pay military personnel on 15 October if the funding lapse is not resolved, a Pentagon official told the BBC.

Senator Mark Kelly, an Arizona Democrat, stood by the Democratic line on Sunday, saying on NBC's Meet the Press that he won't back down from his party's demand to reinstate federal healthcare subsidies in the budget now, not later.

And as for the layoffs, Kelly said Republicans "don't have to do this, they don't have to punish people".

Republican Senator Lindsey Graham of South Carolina told NBC's Meet the Press that he will not vote to extend the subsidies.

Vance blamed the Democrats when speaking to Fox, saying: "This is not a situation we relish, [these layoffs] are not something we're looking forward to, but the Democrats have dealt us a pretty difficult set of cards."

As lawmakers continue battling over the budget, more government services are feeling the effect of the shutdown.

Several Smithsonian museums, research centres and the National Zoo in Washington DC closed on Sunday after funding to keep them open ran out. (BBC)