President Donald Trump says that "beginning today" the US will get back "control of its borders", after signing an executive order to build a wall along the country's southern border and another strengthening the enforcement of immigration laws.
SEE ALSO: Construction of Trump's border wall to begin 'within months'
In a speech at the Department of Homeland Security, Trump says his administration will be working in partnership in Mexico to improve safety and economic opportunity for both countries and will have "close coordination" with Mexico to address drug smuggling.
"We're going to save lives on both sides of the border," he said.
The new president spoke shortly after signing executive orders to strengthen border security and crack down on immigrants living in the US illegally.
It will set in motion the construction of his proposed border wall, a key promise from his 2016 campaign.
"We are in the middle of a crisis on our southern border: The unprecedented surge of illegal migrants from Central American is harming both Mexico and the United States," Trump said in his remarks.
"And I believe the steps we will take starting right now will improve the safety in both of our countries," Trump said, adding: "A nation without borders is not a nation."
White House spokesman Sean Spicer said the wall would help protect Americans.
"Building this barrier is more than just a campaign promise. It's a common sense first step to really securing our porous border," he said.
"This will stem the flow of drugs, crime, illegal immigration into the United States."
He said the orders will strip federal money from so-called sanctuary cities and end a "catch and release" policy of previous administrations.
In an interview with ABC News on Wednesday, Trump said construction on the wall would start within months, with planning starting immediately, and that Mexico would pay back to the United States "100 per cent" of the costs.
Mexican officials have said they will not pay for the wall.
During a White House briefing, Spicer referred to the wall as "a large physical barrier on the southern border."
"Building this barrier is more than just a campaign promise, it's a common-sense first step to really securing our porous border," Spicer added. "This will stem the flow of drugs, crime, illegal immigration into the United States."
Trump's actions could fundamentally change the American stance on immigration, as well as further testing relations with Mexico.
Spicer said Trump's goal was to get the wall project started as quickly as possible using existing government funds and then work with the Republican-led Congress on further appropriations.
"We'll be reimbursed at a later date from whatever transaction we make from Mexico," Trump told ABC on Wednesday.
"I'm just telling you there will be a payment. It will be in a form, perhaps a complicated form. What I'm doing is good for the United States. It's also going to be good for Mexico. We want to have a very stable, very solid Mexico."
Trump made cracking down on illegal immigration a key element of his presidential campaign, with supporters at his rallies often chanting: "Build the wall."
The cost, nature and extent of the wall remain unclear.
Trump last year put the cost at "probably $8 billion," although other estimates are higher, and he said the wall would span 1,000 miles (1,600 km) because of the terrain of the border.
Trump said his directive would also end the practice known by critics as "catch and release" in which authorities apprehend illegal immigrants on US territory but do not immediately detain or deport them.
The directives also include hiring 5,000 more US Customs and Border Protection agents used to apprehend people seeking to slip across the border and tripling the number of US Immigration and Customs Enforcement agents used to arrest and deport immigrants living in the United States illegally.
They also create more detention space for illegal immigrants along the southern border to make it easier and cheaper to detain and deport them.
Trump, who in announcing his presidential bid in June 2015 accused Mexico of sending rapists and criminals into the United States, has also threatened to slap hefty taxes on companies that produce in Mexico for the US market and to tear up the North American Free Trade Agreement among Mexico, Canada and the United States.
Trump and Mexican President Enrique Pena Nieto are due to meet next week.
Trump is expected to take additional steps in the coming days to limit legal immigration, including executive orders restricting refugees and blocking the issuing of visas to people from several Muslim-majority Middle Eastern and North African countries including Syria, Sudan, Somalia, Iraq, Iran, Libya and Yemen.
The intent of those proposals is to head off Islamist violence in the United States, although critics have said it soils America's reputation as a welcoming place for immigrants of all stripes.
Take your Radio, Podcasts and Music with you
