WASHINGTON — President Donald Trump said Wednesday that he is directing the opening of a detention center at Guantanamo Bay to hold up to 30,000 migrants who are living illegally in the United States.

Trump made the announcement right before he signed the Laken Riley Act into law as his administration’s first piece of legislation. The bipartisan measure means that people who are in the U.S. illegally and are accused of theft and violent crimes would have to be detained and potentially deported even before a conviction.

“We’re going to send them out to Guantanamo,” the president said in the White House East Room. He did not elaborate.

The U.S. military base has been used to house detainees from the U.S. war on terrorism.

The Laken Riley Act was described by Trump as a “landmark law” and “tremendous tribute” to the slain Georgia nursing student for whom it is named.

Laken Riley, 22, went out for a run in February 2024 and was killed by Jose Antonio Ibarra, a Venezuelan national who was in the country illegally. Ibarra was found guilty in November and sentenced to life without parole.

“She was a light of warmth and kindness,” Trump said during a signing ceremony that included Riley’s parents and sister. “It’s a tremendous tribute to your daughter what’s taking place today, that’s all I can say. It’s so sad we have to be doing it.”

He added, “It’s a landmark law that we’re doing today. It’s going to save countless lives.”

The measure quickly passed the new Republican-controlled Congress with some Democratic support even though immigrants rights advocates said it possibly could lead to large roundups of people for offenses as minor as shoplifting. Trump has pledged that his administration will carry out the largest deportation effort in U.S. history.

Trump, who won back the White House by tapping into public anger over illegal immigration, has made the promised crackdown a centerpiece of his political career, and is now suggesting the new law might only be the beginning.

The swift passage of the legislation and Trump’s signing nine days after taking office adds to the potent symbolism for conservatives. To critics, the measure has taken advantage of a tragedy and could lead to chaos and cruelty while doing little to fight crime or overhaul the immigration system.

Sen. John Fetterman, D-Pa., a co-sponsor, attended the signing ceremony.

“I believe a secure border creates a more secure nation and it’s just common sense,” he said in a statement, adding that he was elected “to work with both sides of the aisle.”

Federal officials would have to detain any immigrant arrested or charged with crimes such as theft or assaulting a police officer, or offenses that injure or kill someone. State attorneys general could sue the U.S. government for harm caused by federal immigration decisions — potentially allowing the leaders of conservative states to help dictate immigration policy set by Washington.

Ibarra had been arrested for illegal entry in September 2022 near El Paso, Texas, and released to pursue his case in immigration court. Federal officials say he was arrested by New York police in August 2023 for child endangerment and released. Police say he was also suspected of theft in Georgia in October 2023 — all of which occurred before Riley’s killing.

Some Democrats have questioned whether it is constitutional. Immigrant advocates are bracing for mass detentions that they say will mean costly construction of immigration lockup facilities to house the people arrested.

“They don’t just get to celebrate. They get to use this for their mass deportation agenda,” Naureen Shah, deputy director of government affairs in the equality division of the American Civil Liberties Union, said of the act’s supporters.

The ACLU says the act can allow people to be “mandatorily locked up — potentially for years — because at some point in their lives, perhaps decades ago, they were accused of nonviolent offenses.”

Hannah Flamm, interim senior director of policy at the International Refugee Assistance Project, said the measure violates immigrants’ basic rights by allowing for detaining people who have not been charged with wrongdoing — and not even convicted. Still, she said, “The latent fear from the election cycle of looking soft on crime snowballed into aiding and abetting Trump’s total conflation of immigration with crime.”

Flamm said it is likely to be challenged in court. But she also predicted that a need to pay for more immigration detention centers will give advocates a chance to challenge how federal funds are appropriated to cover those costs.

“I think it is pivotal to understand: This bill, framed as connected to a tragic death, is pretext to fortify a mass deportation system,” Flamm said.

The signing follows a flurry of first-week executive orders by Trump that are meant to better seal off the U.S.-Mexico border and eventually deport millions of immigrants without permanent U.S. legal status. The administration has also canceled refugee resettlement and says it may attempt to prosecute local law enforcement officials who do not enforce his new immigration policies.

“We’re tracking down the illegal alien criminals and ... we’re throwing them the hell out of our country,” Trump said. “We have no apologies, and we’re moving forward very fast.”