WASHINGTON (Reuters) - U.S. President Donald Trump said on Wednesday the United States could send as many as 15,000 troops to the border with Mexico, as he hardens his stance against a caravan of migrants fleeing violence and poverty in Central America.

The numbers cited by Trump are significantly higher than defense officials have disclosed. The Pentagon said on Monday it was deploying more than 5,200 troops to the border but that the number would rise. On Wednesday, it said more than 7,000 troops would support the Department of Homeland Security along the border.

Several groups, including the American Civil Liberties Union, have accused Trump of politicizing the military ahead of next week’s congressional elections with his plans to use active military personnel to buttress border patrol efforts.

“As far as the caravan is concerned, our military is out ... We’ll go up to anywhere between 10 and 15,000 military personnel, on top of Border Patrol, ICE and everybody else at the border,” Trump told reporters at the White House.

Trump did not say how many of those 15,000 would be National Guard. There are already 2,100 U.S. National Guard forces at the border, sent after a previous Trump request in April, and they are authorized to go up to 4,000.

If 15,000 troops were drawn into the effort, it would mean there would be more U.S. troops on the border with Mexico than there are in Afghanistan, which has become America’s longest conflict.

Trump has sought to use immigration as an issue to motivate Republican voters ahead of the Nov. 6 elections, where Republicans will seek to maintain control of both congressional chambers.

U.S. President Donald Trump speaks during the "Our Pledge to America's Workers" event at the White House in Washington, U.S., October 31, 2018. REUTERS/Kevin Lamarque

As a presidential candidate before the U.S. election in 2016, Trump promised to harden immigration laws and build a wall along the southern border with Mexico, but implementation of his signature campaign promise has been slow.

A caravan of Central American migrants estimated to number at least 3,500 people left Honduras in mid-October and is now in southern Mexico on its way to the U.S. border.

“WE DON’T DO STUNTS”

Before Trump’s comments, U.S. Defense Secretary Jim Mattis on Wednesday rejected criticism that deploying thousands of troops to the border with Mexico was a political stunt.

“The support that we provide to the secretary for homeland security is practical support based on the request from the commissioner of customs and border police, so we don’t do stunts in this department,” Mattis said after a meeting with his South Korean counterpart at the Pentagon.

Republican lawmakers and other Trump supporters have applauded the deployment. But critics argue Trump has manufactured a crisis to drive Republican voters to the polls.

“The move to send 5,200 active duty troops to the southern border is a craven political stunt that sets a bad precedent and is arguably an abuse of power,” said Kelly Magsamen, a former senior Pentagon official who is currently with the Center for American Progress left-leaning think tank.

Trump’s decision to call in the military appears to be a departure from past practice. In recent years, such operations have been carried out by National Guard forces, largely part-time military members often called upon to respond to domestic emergencies.

A U.S. official told Reuters that as of Wednesday the Pentagon had identified more than 7,000 active-duty troops, which included about 2,000 on standby, that could be deployed to the border with Mexico if needed.

Many basic questions remained unanswered days after the Pentagon announcement, including the scope of the mission as well as the Pentagon’s assessment of any threat posed by arriving migrants.