Trump calling for 20 percent tax on imports from Mexico to pay for border wall

US President Donald Trump wants to pay for his proposed southern border wall by slapping a 20 percent tax on imports from Mexico.

White House spokesman Sean Spicer said Mr Trump has discussed the idea with congressional leaders and wants to include the measure in a comprehensive tax reform package.

Mr Spicer spoke to reporters on Air Force One as Mr Trump flew back from a Republican retreat in Philadelphia.

He said taxing imports from Mexico would generate US$10 billion (A$13 billion) a year and "easily pay for the wall."

Mr Spicer said discussions are continuing with lawmakers to make sure the plan is "done right" but said it "clearly provides funding" for the wall.

The revelation came after Mexican President Enrique Pena Nieto cancelled a planned meeting with Mr Trump over the proposal to make Mexico pay for the wall. 

Mr Trump claimed this morning the cancellation was by mutual consent and said any meeting would have been "fruitless" in any case.

"The President of Mexico and myself have agreed to cancel our planned meeting for next week," Mr Trump said. 

"Unless Mexico is going to treat the United States fairly - with respect - such a meeting would be fruitless. And I want to go a different route."

The White House earlier said it was looking for an opportunity to reschedule Mr Trump's meeting with Mr Pena Nieto.

"We will look for a date to schedule something in the future. We will keep the lines of communication open," Mr Spicer said.

Mr Pena Nieto announced he would not be meeting with Mr Trump on Twitter.

"We informed the White House this morning that I will not attend the working meeting scheduled for next Tuesday," the Mexican leader said.

"Mexico reiterates its willingness to work with the United States to reach agreements in both nations' interests."

Mr Trump had challenged Mr Pena Nieto on Twitter to cancel the visit if he was unwilling to pay for the wall. 

Earlier, Mr Pena Nieto demanded "respect" for his country in a nationally televised address.

"I regret and condemn the decision of the United States to continue construction of a wall that, for years, has divided us instead of uniting us," Mr Pena Nieto said.

"I have said it time and again: Mexico will not pay for any wall."

Mr Trump has already ordered work to begin on building the wall, and yesterday admitted it would be funded with US taxpayer dollars.

In his first sit-down interview since being inaugurated, Mr Trump said the wall will be good for the US and Mexico.

He said the American taxpayer would foot the bill, until Mexico decides to pay.

"There will be a payment, it will be in a form, perhaps complicated form. And you have to understand what I’m doing is good for the United States. It’s going to be good for Mexico," he told ABC News US.

The US leader instructed officials to begin to "plan, design and construct a physical wall along the southern border" and - perhaps more problematically - see how it could be funded.

"A nation without borders is not a nation," Mr Trump said, echoing former president Ronald Reagan, as he visited the Department of Homeland Security to sign two executive orders.

"Beginning today, the United States of America gets back control of its borders."

During his election campaign, Mr Trump pledged to "build that wall' across the 3200-kilometre border between the United States and Mexico.

Some of the border is already fenced, but the president said a wall is needed to stop illegal immigrants entering from Latin America.

Experts have voiced doubts about whether a wall would actually slow illegal immigration, or if it is worth the billions it is expected to cost.