President Donald Trump has said Mexico will “absolutely, 100%” reimburse the US for the wall he plans to build on the southern border.
In an interview with ABC News, the new Republican president said planning was underway for construction would start within months.
He is expected to sign several executive orders on immigration and border security this week.
The measures are likely to restrict refugee access.
“We’re going to be starting those negotiations relatively soon. And we will be – in a form – reimbursed by Mexico,” Mr Trump told ABC News.
“I’m just telling you that there will be a payment. It will be in a form – perhaps a complicated form – and you have to understand. What I’m doing is good for the United States.”
“It’s also going to be good for Mexico”, he added.
Mr Trump tweeted on Wednesday morning: “Big day planned on national security tomorrow. Among many other things, we will build the wall!”
Meanwhile, the Dow Jones traded above 20,000 for the first time, as traders bet that Mr Trump’s policies will boost the economy.
Building a 2,000-mile wall along the Mexican border was one of his key proposals during the presidential election campaign.
Mr Trump initially said Mexico would pay upfront for the wall, which he estimated would cost about $8bn (£6.4bn).
He has since said the US would recoup the costs from its neighbour at a later date.
But Mexico’s president and senior officials have said that they will not fund any wall.
Mr Trump could also take action this week forcing so-called US sanctuary cities to co-operate with authorities on deporting illegal immigrants.
“Sanctuary cities” are places that don’t arrest or detain immigrants living in the country illegally.
Meanwhile, White House press secretary Sean Spicer denied reports of a draft White House order raising the possibility that overseas “black site” CIA-run prisons could be reopened.
The Associated Press reported the document asked senior national security officials whether the president should “reinitiate a program of interrogation of high-value alien terrorists to be operated outside the United States”.
It is not clear where the document came from.
Later this week, Mr Trump is expected to announce immigration restrictions from seven African and Middle Eastern countries, including Syria, Yemen, and Iraq.
He is also likely to halt access to the country for some refugees – until the vetting process can be made more rigorous.
Trita Parsi, from the National Iranian American Council, said: “He called for a Muslim ban and is now taking the first steps to implement one. This will not stand. The American people are better than this.”
But one of Mr Trump’s advisers on the transition team at the Department of Homeland Security, James Carafano, said the new measures should not be seen as anti-Muslim.
“If they’re based on security concerns, of course they have nothing to do with a person’s actual religion,” said Mr Carafano, who is from the conservative Heritage Foundation think-tank in Washington.
Voter fraud probe
Meanwhile, Mr Trump has promised a “major investigation into voter fraud”, after making claims about millions of illegal ballots.
He said the inquiry would include “those registered to vote in two states, those who are illegal”.
Mr Trump also said the probe would focus on “those registered to vote who are dead (and many for a long time)”.
He has claimed that up to five million illegal votes were cast for Hillary Clinton but has offered no evidence.
Mr Trump also took to Twitter to express his concern about the level of violence in Chicago.
He threatened to “send in the Feds” – federal authorities – if the city did not “fix the horrible carnage” taking place.
Meanwhile, the Dutch government has said it will set up an international fund to counter the effects of Mr Trump’s ban on US funding for abortions in developing countries.