Acting White House chief of staff Mick Mulvaney said Sunday that President Donald Trump threatened to close the U.S.-Mexico border because he "will do everything he can" for border security, putting the blame on Democrats for not giving "any additional money ... (or) additional people" to address the issue.

"Why are we talking about closing the border? Because, not for spite and not to -- not to try and -- and undo what's happening, but to simply say, look, we need the people from the ports of entry to go out and patrol in the desert where we don't have any wall," Mulvaney said on "This Week" Sunday. "We need border security, and we're going to do the best we can with what we have.

"The Democrats will not give any additional money to do this. They won't give us any additional people, and, importantly, they will not change the law that is acting as this giant magnet for these people from South and Central America to come into this country. Faced with those limitations, the president will do everything he can. If closing the ports of entry means that, that's exactly what he intends to do."

In a series of tweets on Friday, Trump said that he would be closing the southern border, or large portions of it, this coming week "if Mexico doesn’t immediately stop ALL illegal immigration coming into the United States" through the country. He had previously threatened to close the border last October, just ahead of the 2018 midterm elections.

"Mexico is going to have to do something; otherwise, I’m closing the border. I’ll just close the border," Trump said at an event Friday. "And with a deficit like we have with Mexico and have had for many years, closing the border will be a profit-making operation."

At a later event on Friday, Trump told reporters in Florida that the United States has "run out of space" for migrants and that "Mexico can stop it so easily."

President Donald Trump listens in the Diplomatic Reception Room of the White House, March 25, 2019, as Israeli Prime Minister Benjamin Netanyahu speaks.(Susan Walsh/AP) President Donald Trump listens in the Diplomatic Reception Room of the White House, March 25, 2019, as Israeli Prime Minister Benjamin Netanyahu speaks.

On Friday, Mexico’s foreign minister, Marcelo Ebrard, tweeted, according to a translation by ABC News, "Mexico does not act on the basis on threats. We are great neighbors. If not, tell the million and a half Americans that choose our country as home, the biggest community outside of the USA."

"Your response to the Mexican government?" Karl asked Mulvaney on "This Week."

"The same response we give to all of our -- of our friends to the south, which is, we need your help. We need more action. Mexico could be doing more. El Salvador could be doing more. Honduras could be doing more. We do give these countries hundreds of millions of dollars in aid and we need them to do more," the acting chief of staff said.

Mulvaney said that Mexico "has taken some good steps," but that it’s not enough.

"I think you’ve saw a record number of people returned to Mexico over the past week. That’s a move in the right direction. But when you're dealing with 100,000 people a month, taking a couple hundred people a day doesn't solve the problem," he said.

Late Friday night, the Trump administration announced it would cut all bilateral assistance to El Salvador, Honduras and Guatemala, the three Central American countries collectively known as the Northern Triangle that are the primary source of migrants seeking to enter the United States.

"At the secretary’s instruction, we are carrying out the president’s direction and ending FY [fiscal year] 2017 and FY 2018 foreign assistance programs for the Northern Triangle. We will be engaging Congress as part of this process," a State Department spokesperson told ABC News.

For years, the United States has worked with these countries, trying to address the the problems there that cause migrants to leave in the first place, like an unstable economy and violence and political corruption.

Earlier on Friday, Trump told reporters in Florida that he had ended aid to the three countries, saying they, along with Mexico, "have done nothing."

"I've ended payments to Guatemala, to Honduras and to El Salvador. No money goes there anymore. We were giving them $500 million," Trump said. "We were paying them tremendous amounts of money, and we're not paying them anymore because they haven't done a thing for us."

On "This Week," Mulvaney said, "We need the -- the Northern Triangle countries to do more about not allowing their people in Mexico. They could help us. We need them to do that. If not, it makes very little sense for us to continue to send them aid."

Karl asked Mulvaney about Department of Homeland Security Secretary Kirstjen Nielsen’s recent trip to the three countries during which she met with the security ministers of each respective country.

After the trip, she signed a "historic agreement" that "aims to better synchronize cooperation between the countries in order to bolster border security, prevent the formation of new migrant caravans, and address the root causes of the migration crisis," according to the press release announcing the compact.

"Literally the next day the president announces he's going to shut down the border and -- and he's going to take back all aid or stop all aid to Central America. How is the president so at odds with his own secretary of Homeland Security on this?" Karl asked Mulvaney.

"He’s not," Mulvaney responded. “You can sign all the memorandums of understanding that you -- you can, you can make all the promises you want but when you're still sending 100,000 people across the southern border, actions speak louder than words. We want to work with Mexico, we want to work with the Northern Triangle countries but we need their assistance."