President Trump on Thursday warned the caravan of migrants heading to the southern U.S. border that they will not be let into the country and urged them to return home and apply for U.S. citizenship through the proper, legal channels.

“To those in the Caravan, turnaround, we are not letting people into the United States illegally. Go back to your Country and if you want, apply for citizenship like millions of others are doing!” Trump tweeted.