President Donald Trump declared Monday the US will begin cutting aid to three Central American countries he accused of failing to stop thousands of migrants heading for the US border. But across his administration there was no indication of any action in response to what he tweeted was a "National Emergy."

For hours on Monday, White House officials were unable to provide an explanation for the president's threats, which reflected both his apparent frustration with the migrant caravan and his determination to transform it into Republican election gains. Federal agencies said they'd received no guidance on the president's declaration, issued as he attempts to make illegal immigration a focus of next month's midterm elections.

If Trump should follow through with his threat to end or greatly reduce US aid, that could worsen the poverty and violence that are a root cause of the migration he has been railing against, critics said.

Trump tweeted, "Sadly, it looks like Mexico's Police and Military are unable to stop the Caravan heading to the Southern Border of the United States." He added without evidence that "criminals and unknown Middle Easterners are mixed in."

"I have alerted Border Patrol and Military that this is a National Emergy," he wrote. "Must change laws!"

Trump's tweets marked the latest escalation of his efforts to thrust immigration politics into the national conversation in the closing weeks of the congressional elections. He and his senior aides have long believed the issue – which was a centerpiece of his winning presidential campaign – is key to revving up his base and motivating the Republican Party voters to turn out in November.

"Blame the Democrats," he wrote. "Remember the midterms."

Trump for months has sought to use foreign aid as a cudgel more broadly, threatening to withhold humanitarian and other aid from "enemies of America" and using it to pressure foreign governments to bend to his will. On Monday, he said he would be making good on his threat.

"Guatemala, Honduras and El Salvador were not able to do the job of stopping people from leaving their country and coming illegally to the US. We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them," he wrote.

He added later at the White House, "We have been giving so much money to so many different countries for so long that it's not fair and it's not good. And then when we ask them to keep their people in their country, they're unable to do it."

However, it was unclear whether the president's tweets had any policy implications.

A Pentagon spokesman, Army Lt. Col. Jamie Davis, said the Pentagon had received no new orders to provide troops for border security. And a State Department official said the agency had not been given any instructions on eliminating or reducing aid to Central American countries.

The Pentagon also said it was going ahead with plans to include Honduras among the South American nations that will be visited this fall by the USNS Comfort, a hospital ship that Defense Secretary James Mattis has dispatched to help relieve stress on medical care systems as a result of refugee flows from Venezuela. The Comfort began treating patients in Ecuador on Monday and is scheduled to make stops in Peru, Colombia and Honduras, according to Pentagon spokesman Col. Rob Manning.

"The deployment reflects the United States' enduring promise of friendship, partnership and solidarity with the Americas," Manning said.

Asked what the administration was doing to operationalize the president's tweet, White House spokeswoman Sarah Huckabee Sanders told reporters Monday evening that "we're continuing to look at all options on the table."

"The president wants to make sure we're doing everything we can to secure and protect our borders and that's exactly what he's been talking about," she said.

It is Congress, not the president, that appropriates aid money. The White House would have to notify Congress if it wanted to cut or re-allocate aid, which could delay or complicate the process.

Rep. Eliot Engel, the top-ranking Democrat on the House Foreign Affairs Committee, said Monday that "my colleagues and I will not stand idly by as this administration ignores congressional intent."

The three countries received about 500 million US dollars from the US in fiscal year 2017. That money funds programs that promote economic development and education, as well as supporting democracy and human rights, among other issues. It was not immediately clear how much money Trump now hopes to cut, though the administration already had been pushing to reduce the government's global aid and foreign operations budget by about 30 percent for fiscal 2019 that began from October 1.

Last month, Vice President Mike Pence said that over the last year alone more than 225,000 people from the three Central American countries had attempted to illegally enter the United States, accounting for more than half of those apprehended at the southern border.

Cutting aid could also undermine what the Trump administration has identified as a key foreign policy goal: challenging China's emergence as a strategic rival in the region.

The governments of Guatemala, Honduras and El Salvador did not immediately respond to Trump's threat. Jimmy Morales, president of Guatemala, planned to travel to Tecun Uman on his country's border with Mexico late Monday.

Read more:

Honduran migrant caravan marches into Mexico despite Trump threats

(Cover photo: Central American migrants, who are part of a caravan of migrants trying to reach the United States, walk on a street as they continue their journey in Tapachula, Mexico, October 22, 2018. /VCG Photo)