President Donald Trump has said the US will “begin cutting off” foreign aid to Guatemala, Honduras and El Salvador over the unfolding migrant crisis.
Mr Trump criticised the countries on Monday for allowing people to leave the region and come “illegally” to the US.
The comments mark the latest attempt by Mr Trump to revive a national conversation about immigration before the US mid-term elections.
The caravan of thousands is now making its way through Mexico towards the US.
In 2017, Guatemala received over $248m (£191m) in US aid. The same year, Honduras received $175m and El Salvador $115m, according to the US Agency for International Development.
Mr Trump accused the migrants of trying to illegally enter the US, but many of the families travelling towards the border are seeking asylum.
The migrants say they are fleeing persecution, poverty and violence in their home countries.
Without offering evidence, Mr Trump has also repeatedly suggested the caravan was politically motivated.
“The Caravans are a disgrace to the Democrat Party. Change the immigration laws NOW!'” he said in an earlier tweet.
GETTY IMAGES: A Honduran child staying in tents in the town of Tapachula as the migrants await processing by Mexican officials
Where are the migrants now?
On Sunday, the migrant caravan reached the town of Tapachula, approximately 37km (23 miles) from Mexico’s southern border with Guatemala.
The Mexican authorities had earlier tried to stop them at a border bridge, but some managed to cross into Mexico illegally by boat over the Suchiate river.
“We have sunburn. We have blisters. But we got here. Our strength is greater than Trump’s threats,” migrant Britany Hernández told AFP news agency.
It is expected to take weeks before the caravan reaches the US-Mexico border, according to US media.
One of the closest border crossings in Brownsville, Texas is still over 1,000 miles (1,600 km) away from Tapachula.
The last leg of their journey will also have to wait until Mexico processes the group, and asylum claims can take up to 45 days.
Why is President Trump reacting so strongly?
Curbing illegal immigration was one of the main campaign promises Mr Trump made when he ran for president.
His Republican Party is facing mid-term elections on 6 November and could be unseated by Democrats in the House of Representatives. Immigration is the most important issue facing the US, say 15% of all voters.
While Mr Trump would not be in favour of allowing thousands of Central American migrants to enter the US, the caravan is exactly the kind of issue that could energise his supporters.
Mr Trump on Monday also urged people to blame Democrats for the border crisis, saying: “Remember the mid-terms”.