That means more than 9,000 troops have already been committed to military operations on the border and Trump, who is prone to hyperbole, on Wednesday said the final number could swell to 15,000 troops.
The Mexican government has, in fact, taken a fairly contradictory stance on helping or hindering the caravan, reflecting the country's balancing act: Officials don't want to irk U.S. President Donald Trump, but Mexicans themselves have long suffered mistreatment as migrants. So their role would largely be limited to activities such as providing helicopter support for border missions, installing concrete barriers and vehicle maintenance, rather than detaining migrants.
Later, Trump added that he is thinking "very seriously" and "immediately" of stopping aid to countries where people in the group of migrants are coming from.
"It's a risky group of people", Trump said of the latest group of a few thousand migrants, who are still deep inside Mexico far from their goal. Several smaller groups, estimated at a combined 1,200 people, are farther away. Officials said that number could reach a maximum of about 8,000 under present plans.
Speaking to reporters outside the White House, Trump denied suggestions that the administration is using "fear mongering" to amplify the threat posed by a group of migrants traveling north through Mexico, some of whom said they intend to seek asylum in the United States.
At first there was just one so-called "caravan" of people seeking to enter the US.
With his eyes squarely on next Tuesday's contests, Trump has rushed a series of immigration declarations, promises and actions as he tries to mobilize supporters to retain Republican control of Congress.
Trump's comments on Wednesday appeared to catch the Pentagon off guard.
Trump has sought to use immigration as an issue to motivate Republican voters ahead of the November 6 elections, where Republicans will seek to maintain control of both congressional chambers.
Still, the large troop deployment will be limited to performing similar support functions as the National Guard troops Trump has already sent to the border. Officials said they had no plans to deploy as many as 15,000 troops. President Juan Orlando Hernandez was re-elected last November in an election many Hondurans suspected was fraudulent, but was recognized by the United States.
Trump did not back down Wednesday from his proposal to upend the very concept of American citizenship.
Mr Trump has announced he is sending more than 5,000 soldiers to shore up the US-Mexico border as he talks up what he calls a "migrant invasion" to appeal to his right-wing base ahead of the congressional vote next Tuesday.
He also has introduced the issue of ending birthright citizenship through an executive order, a method Speaker Paul Ryan and others have criticized given forceful language in the 14th Amendment.