WASHINGTON - President Donald Trump said on Monday that he has put the American military and border patrol forces on high alert as a caravan of migrants hoping to gain asylum in the United States moves deeper into Mexico and closer to the US border.

"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. I have alerted Border Patrol and Military that this is a National Emergy. Must change laws!" Trump said in a Twitter post. Trump also placed blame on US Democrats for illegal immigration, saying the party's lawmakers repeatedly blocked his initiatives on immigration reform.

"Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws," Trump said, urging Americans to keep the issue in mind when they vote in the November 6 midterm elections.

According to US media reports, the caravan made up of thousands of Hondurans has crossed into Mexico en route toward the US border, where the migrants hope to gain asylum.

AFP adds: President Donald Trump said Monday the United States will begin cutting aid to three Central American nations because of their governments' failure to stop a migrant caravan headed for the US border.

"We will now begin cutting off, or substantially reducing, the massive foreign aid" that the United States provides to Guatemala, Honduras and El Salvador, he said.

"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," he said on Twitter.

"I have alerted Border Patrol and Military that this is a National Emergy (sic). Must change laws!"

It was unclear what formal action, if any, Trump had taken to activate the military or the border patrol.

Thousands of people seeking to escape poverty and violence in their homelands have pushed into Mexico despite efforts to hold back the migrant caravan at a bridge on the Guatemala-Mexico border.

Around 3,000 migrants reached the city of Tapachula in the Mexican state of Chiapas on Sunday after a seven hour trek from the Guatemalan border.

Trump has used the crisis, which comes two weeks before US midterm elections, as a cudgel against Democrats, reviving the immigrant-bashing rhetoric that helped get him elected in 2016.

"Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws! Remember the Midterms!" he tweeted.