US congressional talks over a border security deal have stalled raising the chances of another government shutdown.
Negotiators were hoping for a deal by Monday to give Congress time to pass legislation by Friday, when the federal funding agreement runs out.
Divisions remain a limit on how many undocumented immigrants can be detained and funding for President Trump’s promised border wall with Mexico.
The previous shutdown, lasting 35 days, was the longest in US history.
Hundreds of thousands of workers were furloughed while others in essential services, such as hospital care, air traffic control and law enforcement, worked without pay.
The cost to the US economy was estimated at $11bn (£8.5bn).
It was unclear how the negotiators would try to reach a deal as no further talks were scheduled, Reuters news agency quoted an unnamed source as saying.
What is the latest impasse about?
The 17 Republican and Democratic negotiators from the Senate and the House have been holding talks to reach a border security agreement that can be accepted by Congress.
The latest impasse seems to be centred on a Democratic demand to limit the number of undocumented migrants already in the US who can be detained by Immigration and Customs Enforcement (ICE).
Democrats planned to cap the number of beds at detention centres at 16,500.
By doing that, they hoped to force ICE to focus on detaining irregular migrants with criminal records instead of those who have overstayed their visas.
They had also been looking at between $1.3bn and $2bn in funding for Mr Trump’s proposed border wall, a long way off the $5.7bn the president has been demanding.
Lead Republican negotiator Senator Richard Shelby said on Sunday he was “not confident we’re going to get there”.
“I’ll say 50-50 we get a deal,” he told Fox News, adding: “The spectre of a shutdown is always out there.”
However one of the Democratic negotiators, Jon Tester, said he remained hopeful a deal could be reached in time to avoid a new shutdown.
“It’s a negotiation. Negotiations seldom go smooth all the way through,” he told Fox News Sunday.
Why is there a risk of another shutdown?
On 25 January President Trump agreed to a three-week spending deal to end the shutdown and allow Congress to reach agreement.
Mr Trump had made stopping the influx of undocumented immigrants the focus of his 2016 campaign – and a priority while in office.
His administration had cracked down on immigrants living illegally in the US by aggressively conducting deportations.
The president has backed away from his calls to make Mexico pay for a concrete wall along the border. But during his State of the Union speech last Tuesday he insisted on a “smart, strategic, see-through steel barrier”.
What would happen in a shutdown?
Federal agencies including the Homeland Security, State, Agriculture and Commerce Departments could lose access to money and begin to close down again, affecting about 800,000 federal employees, who would go unpaid.
During a shutdown, essential services – including border protection, hospital care, air traffic control, law enforcement and power grid maintenance – continue to operate, with workers being required to show up.
Last time, some employees continued to work unpaid but many others called in sick.