Democrats and Republicans have reached an agreement in principle over border security to fund the US government and avert another partial shutdown.

Lawmakers said the deal had been struck in a closed-door meeting in Washington.

No details have been released. Talks had stalled on the detention of undocumented migrants and funding for President Donald Trump’s border wall.

Speaking late on Monday, he did not say whether he would back the deal. “We’re building the wall anyway,” he stressed.

He told supporters in El Paso, Texas, that he had had no time to study the agreement, but stressed that he would “never sign a bill that forces the mass release of violent criminals”.

A bill must be approved by Friday when funding runs out for some federal agencies. The previous shutdown – the longest in US history – lasted 35 days.

The shutdown’s cost to the US economy was estimated at $11bn (£8.5bn).

What is known about the deal?

It was clinched on Monday evening – after several hours of talks between Democratic and Republican negotiators.

Emerging from the talks, Rep Senator Richard Shelby said all outstanding issues had been resolved.

“We got an agreement on all of it,” he said. He added that staff members would work out the details later in the week.

Reports say the deal includes $1.375bn (£1.07bn) in funding for physical barriers – far short of the $5.7bn President Trump has been demanding.

Democrats were also demanding to limit the number of undocumented migrants already in the US who can be detained by Immigration and Customs Enforcement (ICE).

It was agreed to bring down that number to 40,250 from the current 49,057, reports say.

Why is there the 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 an agreement.

That funding ends at midnight on Friday.

Mr Trump made building a wall on the border with Mexico one of his key promises in the 2016 campaign.

The president has backed away from calls to make Mexico pay for a concrete wall but during his State of the Union speech last Tuesday – delayed because of the previous shutdown – he insisted on a “smart, strategic, see-through steel barrier”.

He has previously threatened to declare a national emergency and fund the wall without Congress. But this idea is disliked even by some fellow Republicans, and Democrats are likely to challenge it in the courts.