PALM BEACH, FLORIDA (NYTIMES, BLOOMBERG) - President Donald Trump said on Friday (March 29) that there would be a "very good likelihood" that he will seal off the US border with Mexico next week, escalating a sustained berating of a country he blames for being unable to stop the flow of migrants attempting to make their way north.

"I will close the border if Mexico doesn't get with it," Trump said to reporters who had gathered at Mar-a-Lago, his winter retreat in Florida. "If Mexico doesn't stop it."

Trump has threatened to close off the border several times before and has not followed through. But his comments Friday signalled a new escalation as his administration confirmed that it would review ways to reshuffle Border Patrol agents, shut down traffic lanes and close ports of entry at the south-west border.

He began the day with a morning tweet saying that he would close the border "next week," and then told reporters that he was prepared to close off trade and commercial ports of entry.

A full or partial sealing of the border would effectively close off the United States from one of its largest trading partners, but it could leave American citizens who cross back and forth with a sluggish or potentially nonexistent system of returning to the United States.

"If they don't stop it, we will keep the border closed," Trump said. "I'm not playing games."

The president has been emboldened since the release of a report by the special counsel, Robert Mueller, found that his campaign had not cooperated with the Russian government. And a partisan upholding of his national emergency declaration over a wall along the south-western border has prompted Trump to ratchet up harsh words against immigration as he seeks to galvanize supporters ahead of the 2020 presidential election.

As he engaged in multiple photo opportunities throughout the day, Trump's actions and comments indicated that his mind was not on the scenes at hand but on immigration.

"How are we doing at the border?" he asked a military official on a tour of Lake Okeechobee, the site of a restoration project in the central part of the state.

During a meeting at Mar-a-Lago to announce that Linda McMahon, who has led the Small Business Administration, had resigned, he again turned to immigration. "We have the most laughed-at immigration laws of anywhere in the world," Trump said to reporters as he and McMahon sat in the ornate front room of the club.

"They're the Democrats' laws, and I got stuck with them."

Trump told reporters that he would consider shutting down ports along the border, a decision that could imperil the transit of goods between the United States and Mexico.

According to government figures, Mexico is the United States' third-largest trading partner, with US$557.6 billion worth of products flowing across the border in both directions. A move by Trump to shut down or dramatically curb trade with Mexico would pose significant risks to the US economy.

It would also represent a stunning reversal in trade relations between the two countries, which last August put their differences aside to renegotiate their portion of the North American Free Trade Agreement. The new deal, known as the United States-Mexico-Canada-Agreement, still needs to be approved by Congress.

The president lamented Mexico making a "fortune" off the United States, and said Mexico's immigration laws were the "strongest immigration laws of anywhere in the world." (Mexico is much weaker than the United States at enforcing its border laws.)

Americans would feel the effects in other ways. Border control agencies are already reviewing ways to slow down immigration processing at the border.

A senior Homeland Security official confirmed Friday that shutting down ports of entry along the south-west border is "on the table" to handle the surge in migrants seeking asylum.

Mexican President Andres Manuel Lopez Obrador, speaking in Spanish, told reporters that "we are going to help, we want to have a good relationship with the United States government. We are not going to enter in controversy."

He said that some of Trump's complaints are related to politics and "the electoral process."

Apprehensions of undocumented immigrants spiked in February to more than 76,000, an increase of more than 39,000 compared to a year earlier, according to US Customs and Border Protection.

More than half were families or unaccompanied children, the agency reported.

Homeland Security Secretary Kirstjen Nielsen said in a letter to Congress sent on Thursday that apprehensions will near 100,000 this month, and that her agency faces a "system-wide meltdown."

There are 4,700 migrant children in detention facilities run by Customs and Border Patrol, she wrote, calling the figure "a symptom of a broken system."

"DHS facilities are overflowing, agents and officers are stretched too thin, and the magnitude of arriving and detained aliens has increased the risk of life-threatening incidents," she wrote.

She asked Congress for more money to build detention facilities for the migrants, and also wants the authority to rapidly deport children from Central America "if they have no legal right to stay."

Nielsen's agency is required to hand off most children it apprehends to shelters run by the Department of Health and Human Services, which she said in her letter is also running out of space.

A senior US administration official told reporters in a conference call that the Department of Homeland Security is moving border agents from US ports of entry on the border to patrol areas between them, where most illegal border crossings happen.

The official said no preparations are yet being made to close the border, but that if the flow of migrants continues to increase the US might "degrade" operations at ports.

Most congressional Democrats and some Republicans have disagreed that there was an emergency.

Congress passed a resolution earlier this month disapproving of Trump's plan to divert money from the Pentagon to construction of a border wall.

Trump vetoed the resolution and Democrats couldn't muster the votes to override him.