President Donald Trump on Friday threatened to "close" the nation's southern border with Mexico next week.

Trump did not offer any details about what such a closure would entail. The president has previously issued similar threats; but his missive Friday appeared to mark the first time he attached a timetable to such a statement.

The DEMOCRATS have given us the weakest immigration laws anywhere in the World. Mexico has the strongest, & they make more than $100 Billion a year on the U.S. Therefore, CONGRESS MUST CHANGE OUR WEAK IMMIGRATION LAWS NOW, & Mexico must stop illegals from entering the U.S.... — Donald J. Trump (@realDonaldTrump) March 29, 2019

....through their country and our Southern Border. Mexico has for many years made a fortune off of the U.S., far greater than Border Costs. If Mexico doesn’t immediately stop ALL illegal immigration coming into the United States throug our Southern Border, I will be CLOSING..... — Donald J. Trump (@realDonaldTrump) March 29, 2019

....the Border, or large sections of the Border, next week. This would be so easy for Mexico to do, but they just take our money and “talk.” Besides, we lose so much money with them, especially when you add in drug trafficking etc.), that the Border closing would be a good thing! — Donald J. Trump (@realDonaldTrump) March 29, 2019

The tweets came a day after Mexican President Andres Manuel Lopez Obrador said that illegal immigration is chiefly a problem for the U.S. and Central America to tackle and criticized U.S. immigration policy as "bipolar." Lopez Obrador was responding to a tweet earlier by Trump, who said that Mexico was doing "nothing" to stop the flow of migrants across its border.

On Wednesday, Customs and Border Protection Commissioner Kevin McAleenan, the nation's top border official, said that the nation's southern border is at the "breaking point." It also comes on the heels of the Pentagon's move to direct $1 billion toward building fencing and similar barriers along the 2,000-mile border.

Less than two hours after Trump's tweets, Homeland Security Secretary Kirstjen Nielsen issued a statement declaring that "the system is in freefall" and announcing that she had asked for resources from the department to assist along the southern border, which has seen an influx in apprehensions since the start of the year, especially of families.

"As personnel are reallocated to join the crisis-response effort, there may be commercial delays, higher vehicle wait times at the border, and longer pedestrian lines," Nielsen said. "Despite these impacts, we cannot shirk our responsibility to the American people to do everything possible to secure our country while also upholding our humanitarian values."

Both Sides of the Border View All 21 Images

The secretary also asked Congress for greater authority to deport unaccompanied children more quickly, detain families seeking asylum for longer, and allow immigrants to apply for asylum from their home countries rather than at the U.S. border.

The legal implications of closing the border are extensive: The law would appear to prohibit Trump from preventing American citizens from entering the country from Mexico. The business community, meanwhile, would likely oppose heavy-handed efforts to shutdown trade along the 2,000-mile border.