United States President Donald Trump has walked out of a meeting with Democrat leaders, as both sides try to break a political impasse that has forced a partial government shutdown.

Key points: US government shutdown now on its 19th day

US government shutdown now on its 19th day Mr Trump refused to reopen the government unless Democrats agreed to border wall funding

Mr Trump refused to reopen the government unless Democrats agreed to border wall funding He left a meeting with Ms Pelosi after she again refused his request

The key sticking point is funding for Mr Trump's key policy of building a wall along the border with Mexico.

Mr Trump says Democrat House Speaker Nancy Pelosi said "no" when he asked her if Democrats would approve funding for a barrier, within a month, if he agreed to end the government shutdown.

The meeting was a "total waste of time," he said on Twitter.

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Democratic Senate leader Chuck Schumer accused the President of having a temper tantrum during the meeting.

"He asked [House] Speaker Pelosi, 'Will you agree to my wall?' she said no," Mr Schumer said.

"And he just got up and said, 'Then we have nothing to discuss,' and he just walked out.

"Again, we saw a temper tantrum because he couldn't get his way."

Mr McCarthy said Democrats' behaviour was "embarrassing" after Ms Pelosi refused to agree to funding for the border wall. ( AP: Evan Vucci )

Vice-President Mike Pence said Democrats were "unwilling to even negotiate" with Republicans.

"The President walked into the room and passed out candy," he said.

"I don't recall him ever raising his voice or slamming his hand."

Mr Trump reportedly handed out "a mix" of sweets, including Butterfingers, a chocolate bar with a peanut butter core.

Mr Trump gave out chocolate bars at the meeting, but the mood quickly soured. ( Reuters: Jim Young )

'Get back into the room', Democrats told

Meanwhile, House Minority Leader Kevin McCarthy said the Democrats' behaviour was "embarrassing" and "disturbing".

"The President wants to solve this problem," he said.

"That's why he's put offers on the table, not once have the Democrats offered anything back.

"So I tell the Democrats, 'get back into the room'.

"Let's not leave, let's solve this problem.

"Just as the President said, it doesn't even take 45 minutes."

Ms Pelosi refused to agree to funding for the Mexican border wall. ( AP: Susan Walsh )

Ms Pelosi said Mr Trump did not declare a national emergency, despite the President previously asserting that he had the ability to do so.

"He didn't talk about that," she said.

"It's cold out here and the temperature wasn't much warmer in the Situation Room.

"Our meeting did not last long."

The breakdown in discussions means the shutdown will continue, which has lasted for 19 days after operations ceased on December 22, 2018.

ABC/wires