Possibility of new government shutdown emerges as Republican and Democrat lawmakers clash over immigration enforcement.

Bipartisan border-security negotiations seeking to avert another government shutdown in the United States have broken down in a dispute over immigration detention policies, according to lawmakers and aides.

“The talks are stalled right now,” Republican Senator Richard Shelby told the Fox News Sunday TV programme, adding that he hoped negotiators would return to the table soon.

Efforts to resolve an impasse over border security funding extended into the weekend as a special congressional negotiating panel aimed to reach a deal by Monday.

The group of 17 lawmakers are hoping to reach a deal to allow time for the legislation to pass the US House of Representatives and Senate and get to President Donald Trump by Friday, when federal funding is due to expire.

Democratic Senator Jon Tester played down any breakdown in talks. “It is a negotiation. Negotiations seldom go smooth all the way through,” he told the Fox programme. He said he was hopeful a deal could be reached.

However, no further talks were reportedly scheduled.

Trump agreed on January 25 to end a 35-day partial US government shutdown without getting the $5.7bn he had demanded from Congress for a wall along the border with Mexico, handing a political victory to Democrats.

Instead, a three-week spending deal was reached with congressional leaders to give legislators time to resolve their disagreements about how to address security along the border.

One sticking point has been Democrats’ demands for funding fewer detention beds for people detained by US Immigration and Customs Enforcement (ICE) than the Trump administration seeks. Republicans want to increase the number as part of their drive to speed immigrant deportations.

“I am hoping we can get off the dime later in the day or the morning,” Shelby said. “We have some problems with the Democrats dealing with ICE detaining criminals … They want a cap on them. We don’t want a cap on that.”

While a number of Republicans in Congress have made it clear they would not embrace another shutdown, White House budget Director Mick Mulvaney said he could not rule it out.

“You absolutely cannot,” Mulvaney, who is also Trump’s acting chief of staff, told NBC’s Meet the Press on Sunday. “Is a shutdown entirely off the table? The answer is no.”

But Mulvaney did signal that the White House would prefer not to have a repeat of the last shutdown, which stretched more than a month, left more than 800,000 government workers without paycheques, forced a postponement of the State of the Union address and sent Trump’s poll numbers tumbling.

As support in his own party began to splinter, Trump surrendered after the shutdown hit 35 days without getting money for the wall.

This time, Mulvaney signalled that the White House may be willing to take whatever congressional money comes – even if less than Trump’s goal – and supplement that with other government funds.

“The president is going to build the wall. That’s our attitude at this point,” Mulvaney said on Fox. “We’ll take as much money as you can give us, and we’ll go find the money somewhere else, legally, and build that wall on the southern border, with or without Congress.”

The president’s supporters have suggested that Trump could use executive powers to divert money from the federal budget for wall construction, though it was unclear if he would face challenges in Congress or the courts. One provision of the law lets the Department of Defense provide support for counterdrug activities.

But declaring a national emergency remained an option, Mulvaney said, even though many in the administration have cooled on the prospect. A number of powerful Republicans, including Senate Majority Leader Mitch McConnell, have also warned against the move, believing it usurps power from Congress and could set a precedent for a future Democratic president to declare an emergency for a liberal political cause.

The fight over ICE detentions goes to the core of each party’s view on immigration.

Republicans favour tough enforcement of immigration laws and have little interest in easing them if Democrats refuse to fund the Mexican border wall. Democrats oppose the proposed wall and, in return for border security funds, want to curb what they see as unnecessarily harsh enforcement by ICE.

As most budget disputes go, differences over hundreds of millions of dollars are usually imperceptible and easily solved. But this battle, more than most, is driven by political symbolism – whether Trump will be able to claim he delivered on his long-running pledge to “build the wall” or newly empowered congressional Democrats will be able to thwart him.

Predictably, each side blamed the other for the stall in negotiations.

“We were, you know, progressing well,” Republican Tom Graves said on Sunday on ABC’s This Week. ”I thought we were tracking pretty good over the last week. And it just seems over the last 24 hours or so the goalposts have been moving from the Democrats.”

House Budget Committee Chairman John Yarmuth, a Democrat, countered by telling the same show, “The numbers are all over the place.

“I think the big problem here is this has become pretty much an ego negotiation,” Yarmouth added. “And this really isn’t over substance.”