US President Donald Trump stood firm on Sunday on his demand for billions of dollars to fund a border wall with Mexico, claiming "tremendous" support inside his camp on the contentious issue which has forced a government shutdown now entering its third week.



"We have to build the wall," Trump told reporters as he left the White House for the Camp David presidential retreat. "It's about safety, it's about security for our country.



"We have no choice," he said, warning once more that he may invoke emergency powers to get a wall built without congressional approval.



"I may declare a national emergency, dependent on what's going to happen over the next few days."

Trump has been digging in his heels, demanding billions for a border barrier that Democrats, who now control the House of Representatives, would not provide. He said he is still mulling declaring a national emergency to try to circumvent Congress.

Talks aimed at ending the shutdown were to resume early on Sunday afternoon in Vice President Mike Pence's office, a day after a meeting involving him and representatives of Chuck Schumer and Nancy Pelosi, the top two Democrats in Congress, made little headway.



Trump indicated however, he was not expecting a weekend breakthrough, saying there would be "very serious talks come Monday, Tuesday, Wednesday".

Earlier on Sunday, Trump's press secretary, Sarah Huckabee Sanders, told Fox News cable television, that the president is prepared to bypass Congress if necessary by declaring a national emergency to build his planned wall along the US-Mexico border.

Sanders said the White House has been looking at "every option available" to get the needed money for his wall, adding Trump will do "whatever it takes to protect our borders".

Al Jazeera's Gabriel Elizondo, reporting from Washington, DC, said that everybody is "pessimistic" about the outcome of the talks on Sunday.

Negotiations have been at an impasse over Trump's demands for $5.6bn to fund the border wall.

On Friday, Trump declared he could keep the shutdown going for "months or even years"

'Keep it shut for months or even years'

On Friday, Trump met congressional leaders from both parties amid an impasse over his demand for billions of dollars for a border wall with Mexico.

The standoff has prompted economic jitters and anxiety among some in Trump's own party.

The shutdown has left some 800,000 federal workers sent home or working without pay. Large numbers of federal contractors are also losing pay.

"We won't be opening until it's solved," Trump said. "I don't call it a shutdown. I call it doing what you have to do for the benefit and the safety of our country."

The US president reportedly said he preferred to call the action a "strike".

The US president also said the hundreds of thousands of federal workers who are furloughed or working without pay would want him to "keep going" and fight for border security.

Asked how people would manage without a financial safety net, he declared, "The safety net is going to be having a strong border because we're going to be safe."

Security officers at US airports have reportedly been calling in sick in droves since the shutdown began and their paycheques stopped rolling in.