The US Senate failed for a fifth time on Monday to pass spending measures that would reopen the government.

Competing proposals by Democrats and Republicans were both shot down, failing to meet the 60-vote threshold required.

Donald Trump had reiterated threats of mass layoffs if another vote failed earlier in the day. Thousands of federal employees were furloughed or ordered to work without pay when funding for their agencies ended five days ago.

But the US president hinted that he was open to trying to end the impasse and possibly strike a deal with Democrats who are sticking to demands that the legislation address healthcare. Republicans are pressing for a "clean" funding bill.

The Democratic-led bill to extend the government's funding failed first on Monday with a 45-50 vote. Its Republican counterpart then fell short at 52-42.

Soon after the vote, Trump took to social media to blame Democrats for shutting down the government.

"I am happy to work with the Democrats on their Failed Healthcare Policies, or anything else, but first they must allow our Government to re-open. In fact, they should open our Government tonight!" he posted on his Truth Social platform.

Democrats have held out on supporting the Republican-led proposal because they say it undercuts medical access for lower-income Americans.

They want any funding bill to ensure health insurance subsidies for lower-income Americans do not expire and to reverse the Trump administration's cuts to the Medicaid health programme.

Republicans have repeatedly accused Democrats of shutting down the government to provide healthcare to undocumented immigrants - something Democratic leaders deny. They have also said that they will work on the healthcare issue in separate legislation, after the government reopens.

Speaking in the Oval Office on Monday, Trump said he is currently negotiating with Democratic leadership on possible healthcare provisions.

"We have a negotiation going on right now with the Democrats that could lead to very good things. And I'm talking about good things with regard to healthcare," he said.

But Chuck Schumer, the Democrats' leader in the Senate, wrote on X that "THIS ISN'T TRUE".

The White House has warned since the shutdown started last Wednesday that permanent firings of federal employees were "imminent".

Press Secretary Karoline Leavitt echoed that on Monday, saying the Office of Management and Budget was already working with agencies that would have to lay people off.

"We don't want to see people laid off. But unfortunately, if this shutdown continues, layoffs are going to be an unfortunate consequence of that," she said.

Leavitt also called on Democratic lawmakers to relent.

"There's nothing to negotiate. Just reopen the government," she said.

In separate interviews with NBC's Meet the Press on Sunday, the House's top Democrat, Hakeem Jeffries, and top Republican, Speaker Mike Johnson, each blamed the other's party for the continued stand-off.

Jeffries accused Republicans of "lying" about Democrats' intentions in the negotiations "because they're losing the court of public opinion".

But Johnson said Democrats were "not serious" and negotiating in bad faith.

"They're doing this to get political cover," he said.

Recent polling from CBS, the BBC's US news partner, found that Americans view both parties' handling of the shutdown unfavourably, with Trump and congressional Republicans being blamed slightly more for the situation. (BBC)