The president is expected to sign executive orders on Wednesday
US president Donald Trump is set to launch his immigration crackdown with an order enabling construction of his Mexican border wall.
The president is expected to sign several executive orders on Wednesday addressing one of his central campaign messages - that illegal immigration to the US is out of control and threatening the country's security.
As well as taking the first steps towards building what may eventually be a 2,000-mile barrier stretching across the southern US, Mr Trump is also expected to target so-called 'sanctuary cities', where local officials refuse to hand over illegal immigrants for deportation.
He is expected to sign the orders after speaking to workers at the Department of Homeland Security's Washington headquarters.
He tweeted overnight: "Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!".
Big day planned on NATIONAL SECURITY tomorrow. Among many other things, we will build the wall!— Donald J. Trump (@realDonaldTrump) January 25, 2017
Mr Trump would need to get approval from the US Congress for any new funding for the wall - with costs estimated at US$6.5m (€6.06m) per mile for a single-layer fence by the Government Accountability Office.
The billionaire property tycoon said during his campaign and subsequently that Mexico would pay for the wall - a suggestion the country's leaders have repeatedly rejected.
The timetable for the various measures on immigration is reportedly still being finalised, but later this week the president is expected to move on to restricting access to the United States for refugees and some visa holders from Syria, Iraq, Iran, Libya, Somalia, Sudan and Yemen.
The limits on refugees could include a ban lasting months on admissions from all countries until the US State Department and the Department of Homeland Security can increase the intensity of the vetting process.
On the campaign trail, Mr Trump proposed a temporary ban on Muslims entering the United States to protect Americans from terrorist attacks - but the headline promise subsequently disappeared from his website.
Both he and his nominee for Attorney-General, Senator Jeff Sessions, have shifted their focus to those individuals who could pose a danger, rather than any specific ban on people of a certain faith.
It is understood Mr Trump will have to instruct the State Department to stop issuing visas to people from those nations.
Another option at his disposal is instructing US Customs and Border Protection to stop any current visa holders from those countries from coming into the United States.
Immigration hardliners had been growing impatient, piling on the pressure as the new president quietly backed away from a pledge to end protections for nearly 750,000 immigrants brought to the US illegally as children.
These latest orders give the impression of Mr Trump following through on his big pledges - but they will prove hugely controversial, requiring a major shake-up of America's immigration system.