ABOARD AIR FORCE ONE (Reuters) - U.S. President Donald Trump said on Thursday he would probably station a few thousand National Guard troops at the 2,000-mile-long (3,200-km) Mexican border until the wall he wants to build there to keep out illegal immigrants is done.

Members of the U.S Army National Guard monitor the Oculus transportation hub ahead of the U.S presidential election in Manhattan, New York, U.S., November 7, 2016. REUTERS/Andrew Kelly

No funding for the entirety of Trump’s proposed wall is currently in place. Both the Mexican government and the U.S. Congress so far have refused to fully pay for it. Trump vowed as a candidate that he would get Mexico to pay for his wall.

Hounded by headlines about alleged affairs with various women and a continuing probe of possible collusion between his presidential campaign and Russia, Trump has recently escalated the anti-immigrant rhetoric that helped him get elected.

In a storm of Tweets this week, he has warned that illegal immigrants are threatening U.S. security and jobs, a theme that has resonated in the past with conservative Republican voters.

Trump last month signed a federal spending bill from Congress that contained $1.6 billion to pay for six months of work on his wall. He had asked for $25 billion for it.

En route back to Washington from an event in West Virginia where he talked about the 2017 Republican tax overhaul, Trump was asked by reporters how many National Guard troops he wanted at the border. He said: “Anywhere from 2,000 to 4,000.”

He said the administration was looking at the costs. “It depends on what we do,” he said. “We’re looking from 2,000 to 4,000 and probably keep them, or ... a large portion of them, until such time as we get the wall.”

The deployment was likely to aggravate tensions with Mexico, a key U.S. ally that has already expressed concern.

On Wednesday, the administration said it was coordinating with the governors of the four U.S. states that border on Mexico on deploying the Guard, a reserve wing of the U.S. armed forces that is partly under the supervision of state governors.

The Guard would not be involved in law enforcement, but would assist U.S. Customs and Border Protection personnel with stopping illegal immigrants from entering the country, Homeland Security Secretary Kirstjen Nielsen said on Wednesday.

The Pentagon said it set up a Border Security Support Cell “to ensure we surge our capacity to meet the president’s enhanced border security goals,” said a Pentagon spokeswoman.

Speaking with reporters at a press briefing on Thursday, Pentagon officials said they did not yet know where funding for sending Guard troops to the border would come from.

They said other details were still unknown, such as how many troops would be deployed and whether they would be armed.

A Pentagon spokeswoman said the military was looking into possibly building a wall at its Barry Goldwater Air Force Range in the desert in Arizona along the Mexican border.

The administration’s move has drawn criticism from Democrats. “At a time when apprehensions of migrants on our southern border are at a near 50-year low, deploying National Guard troops to the border is far from a logical effort,” Democratic Senator Tom Carper said in a statement.

“It is imperative that this administration sit down with leaders in Congress on both sides of the aisle who want real solutions to our immigration challenges, rather than using political ploys to fire up President Trump’s base and distract from growing controversy,” Carper said.