US president Donald Trump has said his government will begin cutting aid to three Central American countries he accused of failing to stop thousands of migrants heading for the US border.

However, across his administration there was no indication of any action in response to what he tweeted was a “National Emergy” (sic) regarding migrants from Honduras, Guatemala and El Salvador.

White House officials were unable to provide an explanation for the president’s threats, which reflected both his apparent frustration with the migrant caravan and his determination to transform it into Republican election gains ahead of mid-term elections next month.

Critics pointed out that if aid – which totalled $500 million (£384m) in fiscal year 2017 – is reduced to the three countries it could worsen the poverty and violence that are a root cause of the migration he has been railing against.

Trump tweeted: “Sadly, it looks like Mexico’s Police and Military are unable to stop the Caravan heading to the Southern Border of the United States.”

He added, without providing evidence, that “criminals and unknown Middle Easterners are mixed in”.

“I have alerted Border Patrol and Military that this is a National Emergy,” he wrote. “Must change laws!”