Donald Trump threatened Saturday to close the southern border, just as Mexico announced it had not reached a deal with the U.S. on allowing asylum-seekers to stay in the country while they wait for approval.

“Migrants at the Southern Border will not be allowed into the United States until their claims are individually approved in court,” Trump said. Migrants will stay in Mexico, and any that come into the country illegally will be detained rather than released.

Migrants at the Southern Border will not be allowed into the United States until their claims are individually approved in court. We only will allow those who come into our Country legally. Other than that our very strong policy is Catch and Detain. No “Releasing” into the U.S…

— Donald J. Trump (@realDonaldTrump) November 24, 2018

….All will stay in Mexico. If for any reason it becomes necessary, we will CLOSE our Southern Border. There is no way that the United States will, after decades of abuse, put up with this costly and dangerous situation anymore!

— Donald J. Trump (@realDonaldTrump) November 24, 2018

The incoming Mexican government of Andres Manuel Lopez Obrador denied reports Saturday that the country will harbor the migrants as part of a plan with the Trump administration called “Remain in Mexico,” according to the Associated Press.

“There is no agreement of any sort between the incoming Mexican government and the U.S. government,” future Interior Minister Olga Sanchez said in a statement. Lopez Obrador takes office Dec. 1.

A reported 5,000 migrants from Central America, part of the so-called “migrant caravan”, are in Tijuana, Mexico, as they try to seek asylum at points of entry along the California border. The mayor of Tijuana appealed to the United Nations earlier this week for aid in dealing with the migrants, and declared the situation an international humanitarian crisis.

Twitter quickly called Trump out:

Do you understand how ignorant you have to be to become President of a country & still not learn any of its laws? Migrants seeking asylum at the border are doing so legally & your catch & detain policy was thrown out by the courts because it’s unconstitutional. So they can enter.

— Andrew Wortman (@AmoneyResists) November 25, 2018

Our great country was created by & because of immigrants. That is why we were the greatest country in the world. That made us strong.

You do the opposite. And by your own rules you & your kids would be deported.

Are you really that dumb or do you just think your supporters are? pic.twitter.com/zn4NKuuE8p

— Khashoggi’s Ghost (@UROCKlive1) November 25, 2018

Ok, last time. It is legal for someone seeking asylum to walk in to America, and present themselves to the proper authorities. You have been informed of this by the courts, so I have to assume you are intentionally breaking US and international law.

— Jules (@Jules_In_Love) November 25, 2018

They are seeking asylum. Seeking asylum is LEGAL. Maybe you should have sent members of the court to expedite the process instead of sending the military for an election stunt.

— NerdyIntrovert (@megsmonkeybeans) November 25, 2018

Just so we're straight here. You will break the law because you don't like it? Because you think you can? So maybe we can all break the law if we don't like it? Have I got that right? WE HAVE A PROCESS IIN THIS COUNTRY THAT YOU THINK DOESN'T APPLY TO YOU.

— Leann Sweeney (@leannsweeney) November 25, 2018