There could be a Sunday showdown at the Mexican border. Hundreds of Central American migrants are planning to cross the border seeking asylum.

The caravan of buses arrived in Tijuana with Central American migrants, weary after a month of travel. Maria Martinez is seeking asylum in the U.S. after she says gangs of outlaws in El Salvador tried to force her son to join them.

"They threw us on the floor, kicked our faces and said they would kill us," Martinez said. "That's what motivated me to leave my country."

Amid the migrants' pleas for help, President Trump tweeted this week that he had "instructed the Secretary of Homeland Security not to let these large caravans of people into our country."

But it may not be that easy. The U.S. is bound by international law to hear out asylum claims.

"I think most Americans don't understand that you can detain, but you can't deport them," said Texas Congressman Michael McCaul during a Thursday hearing with Homeland Security Secretary Kristjen Nielsen. "If they cross in to U.S., what will you be able to do?"

"Participating in a caravan doesn't give you any additional legal rights," Nielsen said. "If you file a false asylum claim, you will be referred to prosecution."

Nielsen also said the migrants should seek asylum in the first safe country they enter, including Mexico. Many have already done that, at one point the caravan drew up to 1,000 people as it crossed Mexico.

In Tijuana on Thursday, the roughly 400 migrants remaining, are meeting with immigration lawyers, preparing to turn themselves over to border agents on Sunday. Attorney Nora Phillips says she instructing them to tell the truth.

"If you have fraud, then it ends up making it a million times harder for people who actually have asylum claims to take advantage of this process," Phillips said.