WASHINGTON (NYTIMES) - President Donald Trump will order the construction of a Mexican border wall on Wednesday (Jan 25), White House officials said.

He is also mulling plans to stop Syrian refugees from entering the country and to slash immigration of refugees from "terror prone" nations, perhaps as early as this week.

During an appearance at the Department of Homeland Security on Wednesday, Mr Trump plans to sign an executive order to direct federal funds to be shifted towards the building of a wall on the southern border that became a signature promise of his campaign. He has argued that doing so is vital to gaining control over the illegal flow of immigrants into the United States.

This executive order will be signed on the day that Mexico's Foreign Minister Luis Videgaray arrives in Washington to prepare for the visit of President Enrique Pena Nieto of Mexico, who is to meet with Mr Trump at the end of the month. He will be among the first foreign leaders to meet the new president.

Mr Trump is also expected to target legal immigrants as early as this week, the officials said, by halting a decades-old program that grants refuge to the world's most vulnerable people as he begins the process of dramatically curtailing it.

He is considering a policy that would temporarily freeze refugee admissions from Syria and other majority-Muslim nations that are considered "terror prone" and would halve the number of displaced people who can be resettled on American soil.

This would effectively bar the entry of people from Muslim countries - including Afghanistan, Iraq, Somalia and Syria - and might prioritise the admission of those who are Christian religious minorities.

The plan is in line with a ban on Muslim immigrants that Mr Trump proposed during his campaign, arguing that such a step was warranted given concerns about terrorism. He later said he wanted to impose "extreme vetting" of refugees from Syria and other countries where terrorism was rampant, although the Obama administration had already instituted strict screening procedures for Syrian refugees that were designed to weed out anyone who posed a danger.

White House officials described the actions on the condition of anonymity on Tuesday to avoid pre-empting the planned announcement.

Mr Trump is also considering slashing, to 50,000 from 110,000, the number of refugees who could be resettled in the United States this year, they said.

The expected actions drew strong criticism from immigrant advocates and human rights groups, which called them discriminatory moves that rejected the American tradition of welcoming immigrants of all backgrounds.

"To think that Trump's first 100 days are going to be marked by this very shameful shutting of our doors to everybody who is seeking refuge in this country is very concerning," said Mr Marielena Hincapie, the executive director of the National Immigration Law Centre. "Everything points to this being simply a backdoor Muslim ban."

For Mr Trump, whose raucous campaign rallies frequently featured chants of "Build the wall," the directive to fortify the border was not unexpected, although it may not be enough by itself to accomplish the task. Congress would need to approve any new funding necessary to build the wall, which Mr Trump has insisted Mexico will finance, despite its leaders' protestations to the contrary.

The Government Accountability Office has estimated that it could cost US$6.5 million (S$8.5 million) per mile to build a single-layer fence, and an additional US$4.2 million per mile for roads and more fencing, according to congressional officials.

Those estimates do not include maintenance of the fence along the nearly 2,000-mile border with Mexico. Ms Nancy Pelosi of California, the Democratic leader, said she thought even Republicans might balk at spending what she said could be US$14 billion on a wall.

Mr Trump has said that immigration will be on the agenda when he meets with Mr Nieto.

The order to build the wall is likely to complicate the visit of Mr Videgaray, who has a history with Mr Trump. It was Mr Videgaray, then Mexico's finance minister, who orchestrated Mr Trump's visit to Mexico before the election, a move seen by many Mexicans as tantamount to treason.

He was forced to resign because of the fallout, but his reputation was restored after Mr Trump's victory, and he was given the job of foreign minister, in part to capitalise on his relationship with the new American leader.

It is unclear whether Mexican officials were involved in Mr Trump's decision to sign the executive order during Mr Videgaray's visit.

Human rights groups whose leaders have been anticipating Mr Trump's refugee crackdown have already begun preparing legal efforts to halt them.

"We are definitely ready to stand in court and challenge any part of the executive order that flies in the face of our Constitution and our core values," Mr Hincapie said.

Mr Trump's directive is expected to target a programme the Obama administration expanded last year in response to a global refugee crisis, fueled in large part by a large flow of Syrians fleeing their country's civil war. Former President Barack Obama increased the overall number of refugees to be resettled in the United States to 85,000 and ordered that 10,000 of the slots be reserved for Syrians. He set the number of refugees to be resettled this year at 110,000, more than double the 50,000 Mr Trump is now considering.

By the end of last month, more than 25,000 refugees had been resettled, according to State Department figures, meaning Mr Trump would admit only 25,000 more between now and the end of September, when the fiscal year ends.

The refugee resettlement programme, which has long drawn strong support from Republicans and Democrats, became the subject of bitter debate during the presidential campaign. The November 2015 terrorist attacks in Paris stoked fears in the United States, and Mr Trump claimed without evidence that "thousands upon thousands" of Muslim refugees with terrorist mindsets had been "pouring into our country" without proper screening.