WASHINGTON – President Donald Trump said Thursday he would unveil a plan to limit claims of asylum in the United States, saying there was "rampant abuse" of the system.

But he offered no details on the proposal, which was part of a series of immigration announcements he has rolled out in the run-up to next Tuesday's midterm elections.

Trump said people were taking advantage of the asylum process by making false claims of persecution in order to enter the country. He said many end up staying in the country and fail to show up for court proceedings to determine the validity of their asylum claims.

"My administration is finalizing a plan to end the rampant abuse of our asylum system," he told reporters at the White House before leaving for a rally in Missouri, where he is campaigning for Republican Senate candidate Josh Hawley.

Trump has sought to make immigration a central issue in the elections, where Republican control of the House and Senate are up for grabs. The issue could help stir up his core conservative supporters and motivate them to go to the polls, but it also has the potential to turn off moderate voters who are especially crucial in House races this year.

When questioned about the military's role on the border, Trump suggested soldiers could open fire if migrants threw rocks at them.

"They want to throw rocks at our military, our military fights back," the president told reporters. "I told them to consider it a rifle."

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Existing U.S. asylum laws give people entering the country broad authority to claim the need for protection. Trump did not make clear whether he would seek changes in the law, but he did indicate he would be unveiling an executive order.

The 1965 Immigration and Nationality Act states that any foreigner who arrives in the U.S. “whether or not at a designated port of arrival” may apply for asylum. A 1951 United Nations treaty signed by the U.S. states that “refugees should not be penalized for their illegal entry” because their extreme situations sometimes “require refugees to breach immigration rules.”

Trump vowed to build "tent cities" to detain asylum seekers until their court hearings.

“We’re not releasing them into our country any longer ... We’re putting up massive cities of tents," he said. "We're going to hold them right there."

Trump claimed, without evidence, that only 3 percent of people seeking asylum appear for a court hearing, suggesting the rest remain in the country illegally.

But Justice Department data suggest that most migrants appear for court. In 2016, 61 percent of non-detained migrants showed up for their hearing in immigration court, according to that data. In 2012, nearly eight in 10 migrants appeared for the hearing.

Some studies conducted by immigrant advocacy groups have found the court appearance rate is higher among those seeking asylum.

Trump has repeatedly highlighted what he said is a threat posed by a caravan of several thousand Central Americans making its way to the U.S. border. While Trump has portrayed the members of the caravan as a group of "tough" young men, reporters traveling with them have instead described them as families trying to escape poverty and violence.

The Pentagon said Wednesday it would send some 7,000 active duty troops to the border, and the president has said that deployment could expand to between 10,000 and 15,000 troops.

Democrats have accused Trump of using fear mongering on immigration to energize his base.

Rep. Bennie Thompson of Mississippi, the top Democrat on the Homeland Security Committee, called Trump’s speech "a political stunt aimed at whipping up fear and xenophobia just days before the election."

He said the remarks consisted of "outright propaganda and non-stop lies.”

Contributing; John Fritze and Alan Gomez’

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