Trump kept up his almost-daily Twitter attacks on the approaching caravan, calling it a national emergency and said he had alerted the US border patrol and military, AFP reported.
“We will now begin cutting off, or substantially reducing, the massive foreign aid” that the United States provides to the three Central American countries, he said.
Mexican authorities had managed to block the “caravan” of migrants on a border bridge between Mexico and Guatemala, but many later crossed the river below in makeshift rafts before marching north.
The caravan of around 3,000 migrants was heading Monday to the town of Huixtla, around 40 kilometers further on from Tapachula in Chiapas State where they slept Sunday night.
“Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States. Criminals and unknown Middle Easterners are mixed in,” Trump said in one tweet.
“I have alerted Border Patrol and Military that this is a National Emergy (sic). Must change laws!”
US Secretary of State Mike Pompeo also warned that the migrants “may be victimized by human smugglers or others who would exploit them.”
About a thousand migrants, including women and children, were still stranded on a border bridge hoping to enter Mexico legally via Guatemala.
Mexican authorities insisted those on the bridge would have to file asylum claims one at a time in order to enter the country.
And another separate group of about 1,000 Hondurans started their own march across Guatemala, headed for Mexico and then the US. The group of men, women and children gathered in Esquipulas before setting out on foot.
Mexico’s president-elect Andres Manuel Lopez Obrador called for fair treatment of the migrants.
“We don’t want them to face what (Mexicans) face when they need to look for work in the United States,” he said on Twitter.
The caravan left San Pedro Sula in northern Honduras more than a week ago. It has comprised between 3,000 and 5,000 people at various times as it moved through Guatemala, according to various sources.
Guatemalan President Jimmy Morales said more than 5,000 migrants had entered Guatemala from Honduras, but that some 2,000 had since returned home on a fleet of government-chartered buses.
Morales and his Honduran counterpart Juan Orlando Hernandez said after meeting that the march was “violating the borders and the good faith of the states.”
The Honduran president acknowledged that social problems were a contributory factor.
“Without a doubt, we have a lot to do so that our people can have opportunities in their communities,” he said.
The migrants are generally fleeing poverty and insecurity in Honduras, where powerful street gangs rule their turf with brutal violence.
With a homicide rate of 43 per 100,000 citizens, Honduras is one of the most violent countries in the world, according to a Honduran university study.