President Donald Trump said Tuesday that the U.S. military will be used to prevent caravans of illegal immigrants from pouring over the southern border with Mexico. His remarks come as activists intend to illegally bring a roughly 1,000-strong caravan of migrants across the U.S.-Mexico border to claim asylum.

“Until we can have a wall with proper security, we are going to be guarding our border with our military. That’s a big step,” he told reporters at the White House. “We cannot have people flowing into our country illegally, disappearing, and by the way never showing up for court.”

President Trump earlier Tuesday morning said in a tweet that NAFTA and foreign aid are “in play” if Honduras and other countries don’t stop the caravans. The NAFTA threat worked, and Mexico has responded to requests to disperse at least one of the caravans.

Pueblo Sin Fronteras, or People Without Borders, accused President Trump on Monday of “bullying” illegal immigrants.

“Trump is trying to turn Central American refugees and other immigrant communities against each other, and use them as a bargaining chip with Mexico,” the group said in a statement.

Nevertheless, President Trump said he has spoken with U.S. Defense Department Secretary James Mattis about the use of the military to guard the border. The plan will entail using the military until a border wall is constructed. The President applauded Mexican authorities for breaking at least parts of the caravan up “very rapidly” as it moved through Mexico.

“They have very strong immigration laws, as we should have,” he said. “It’s sad for the people in the caravan and it’s sad for the people in the United States.”