WASHINGTON - US President Donald Trump said on Monday that his country will begin cutting off or reducing aid to three countries in Central America, citing migrant caravan heading to the US border.

"Guatemala, Honduras and El Salvador were not able to do the job of stopping people from leaving their country and coming illegally to the US," said Trump in a morning tweet.

"We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them," the US president added.

Regarding the incident as a "national emergency," Trump said in another tweet that he had alerted the US Border Patrol and Military as "it looks like Mexico's Police and Military are unable to stop the Caravan heading to the Southern Border of the United States."

Over the weekend, thousands of migrants, mostly from Honduras, have swarmed into Mexico after passing the Guatemalan border. Media reported that Mexican police, watching vigilantly alongside, did not disturb migrants' journey.

It was the latest among Trump's tweets warning against serious consequences about the migrant people which were heading toward the United States, seeking for asylum.

Official data showed that the Trump administration has sharply slashed aid to the three countries in Central America, projecting a roughly 40-percent plunge in aid in the financial year of 2019 compared with that of 2016.