Donald Trump has stormed out of talks with Democrat leaders over the US government shutdown, calling the meeting a "waste of time".
Trump later tweeted that he had said 'bye-bye' as he left the talks which aimed to find a resolution to the deadlock over funding for the Mexican border wall.
Trump said he could still declare a national emergency as the now 19-day government shutdown threatens to rip the US government apart.
The President called talks with Democrats on Wednesday afternoon local time a "total waste of time", the day after his Oval Office address in which he called for support from the US public and Democrats for a resolution to the impasse.
Just left a meeting with Chuck and Nancy, a total waste of time. I asked what is going to happen in 30 days if I quickly open things up, are you going to approve Border Security which includes a Wall or Steel Barrier? Nancy said, NO. I said bye-bye, nothing else works!
— Donald J. Trump (@realDonaldTrump) January 9, 2019
Speaking to reporters about the tense meeting, Senator Chuck Schumer said Trump stormed out following disagreements about the border wall.
"He said, 'If I open up the government you won't do what I want,'" said Schumer.
"That's cruel, that's callous, and that's using millions of innocent people as pawns.
"A few minutes later, he sort of slammed the table, and when Leader Pelosi said she didn't agree with the wall, he just walked out and said we have nothing to discuss. He said it was a waste of his time."
Vice President Mike Pence denied Schumer's claims, saying Trump never raised his voice or slammed his hand on the table.
However Trump confirmed he had abruptly left the meeting, tweeting: "Just left a meeting with Chuck [Schumer] and Nancy [Pelosi], a total waste of time."
"I asked what is going to happen in 30 days if I quickly open things up, are you going to approve Border Security which includes a Wall or Steel Barrier?"
"Nancy said, NO," Trump said. "I said bye-bye, nothing else works!"
In a national emergency, Trump should be able to draft in defence department resources to build the wall, but this is likely to face a major court challenge.
Before leaving the White House for Capitol Hill, the President told reporters that if Congress would not agree to his demand for $5.7 billion ($A8 billion) border wall funding, "we'll go about it in a different manner".
He said he had the "absolute right to do a national emergency if I want", and that his threshold "will be if I can't make a deal with people that are unreasonable."
The Democrats are only willing to provide $US1.3 billion for border security, including fencing and surveillance, and called the wall "immoral" and unnecessary.
Asked how long he was willing to let the shutdown continue, Trump replied: "Whatever it takes."
The partial government shutdown is creating deep divisions in an already ruptured Congress, with some Republicans ready to vote against Trump on the border wall.
Democrats in the House of Representatives — where the party has the majority — will introduce a vote on a series of bills to reopen key parts of the government this afternoon.
But they will need to gain support from the GOP-majority Senate.
Trump emerged from a lunchtime meeting with GOP politicians saying: "The Republicans are totally unified … There was no discussion of anything other than solidarity."
He then headed to a third round of negotiations with Democrats, but described the talks as "a total waste of time" as they broke down yet again.
But their actions suggested Trump's claim the party was "very, very united" was not entirely accurate.
Republican senators Cory Gardner and Susan Collins, up for re-election in 2020 in the knife-edge states of Colorado and Maine respectively, have called for votes to end the shutdown.
Seven GOP members of Congress crossed the floor to vote last week and even more may support Democrat bills on Wednesday afternoon to reopen the Treasury Department, Internal Revenue Service and other agencies.
"We expect that with each passing day, additional Republicans in the House, as well as Senate Republicans, will publicly express their objection to keeping the government shut down," Democrats conference chairman Hakeem Jeffries told the Washington Post.
"We expect that the number will cross into double figures today and as the week proceeds."