President Donald Trump on Monday said that the United States will substantially reduce financial aid to Guatemala, Honduras and El Salvador as the countries had failed to stop their citizens from leaving and illegally entering America.

In a series of tweets, Trump lashed out at a caravan of thousands of immigrants and asylum-seekers travelling from Central American nations with the aim of entering the US, describing it as a “national emergency”.

The caravan on Monday resumed its journey from southern Mexico, but is still far from the US border. It comprises mostly Hondurans, who say they are fleeing violence and poverty.

“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,” he said on Twitter. “We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them.”

The three Central American nations received about $500 million from the US in fiscal year 2017, AP reported.

Democratic Representative Nita Lowey said the threat to reduce foreign aid “ignores that Congress, not the president, is entrusted by the Constitution with the power of the purse”, reported Reuters. “Cutting funding would make the problem worse, not better,” she said.

White House spokesperson Sarah Huckabee Sanders said the administration was considering “all options on the table” in terms of reducing aid. “The president wants to make sure we are doing everything we can to secure and protect our borders and that’s exactly what he’s been talking about,” she said.

Trump sought to blame the Democrats for not helping the Republican Party change immigration laws. “So unfair to those who come in legally,” he said.

Speaking at a rally in Houston on Monday, Trump also accused Democrats of “encouraging millions of illegal aliens to break our laws, violate our borders and overwhelm our nation”.

A United Nations official on Monday said that the number of people in the caravan could continue to increase, reported USA Today. UN Deputy Spokesperson Farhan Haq told reporters in New York that the caravan now comprises an estimated 7,233 persons, “many of whom intend to continue the march north”.