President Donald Trump said Monday he will move to cut foreign aid to Guatemala, Honduras and El Salvador for failing to stop people “coming illegally into the U.S.”

The threat, made in an early-morning tweet, comes as publicity grows about a caravan of thousands of people weaving its way up through Central America towards the U.S. border.

The caravan formed in the Honduran city of San Pedro Sula. Over the weekend, it crossed the border between Guatemala and Mexico, leading to growing alarm from anti-migrant voices in the U.S.

“Guatemala, Honduras and El Salvador were not able to do the job of stopping people from leaving their country and coming illegally to the U.S.,” Trump tweeted Monday morning. “We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them.”

Guatemala received $249 million of U.S. aid in 2017, according to USAID. Honduras received $175 million, and El Salvador received $115 million.

“Our programs contribute to a safer and more prosperous United States by helping to secure our borders, protect our citizens, and increase economic and business opportunities,” reads a pre-existing statement from Mark Green, the administrator of USAID, on the group’s website. “In addition, evidence suggests it helps mitigate the conditions that drive migrants to make the perilous trip north,” he said.

Trump also claimed without evidence that “unknown Middle Easterners are mixed in” with the crowd of migrants.

“Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States,” Trump tweeted. “Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emergy. Must change laws!”

Trump did not say in his tweets whether cutting foreign aid to Mexico was being considered.

Get The Brief. Sign up to receive the top stories you need to know right now. Please enter a valid email address. Sign Up Now Check the box if you do not wish to receive promotional offers via email from TIME. You can unsubscribe at any time. By signing up you are agreeing to our Terms of Use and Privacy Policy . This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Thank you! For your security, we've sent a confirmation email to the address you entered. Click the link to confirm your subscription and begin receiving our newsletters. If you don't get the confirmation within 10 minutes, please check your spam folder.

Write to Billy Perrigo at billy.perrigo@time.com.