The U.S. military base in Cuba has historically been used to hold terror suspects since 9/11 and current detainees include the accused mastermind of the attack. 

Using it for migrants is the latest symbolic move in Trump's unprecedented crackdown on illegal migration that began the moment he entered office last week. 

Immigration and Customs Enforcement has conducted raids across the country and deportation flights have left the United States daily – with the administration putting out images of the effort.

Trump said the facility with 30,000 beds will be used to keep the 'worst of the worst' migrants under lock and key, and noted how 'tough' it is to escape.

It will include suspects from countries he doesn't trust will detain them when they are deported.

Homeland Security Secretary Kristi Noem floated the plan earlier on Wednesday, but Trump has now put the idea into motion. 

'Today, I'm also signing an Executive Order to instruct the Departments of Defense and Homeland Security to begin preparing the 30,000 person migrant facility at Guantanamo Bay to detain the worst criminal illegal aliens threatening the American people,' Trump said.

He made the announcement while signing the Laken Riley Act at the White House on Wednesday.

Trump added: 'We have 30,000 beds in Guantanamo to detain the worst criminal illegal aliens threatening the American people. Some of them are so bad we don't even trust the countries to hold them because we don't want them coming back. 

'So we're going to send them out to Guantanamo Bay. This will double our capacity immediately, and tough. That's a tough - that's a tough place to get out of.'

The George W. Bush administration opened the facility in 2002 to detain 'illegal enemy combatants' during the 'War on Terror.' Ultimately, successive administrations have negotiated a series of arrangements to transfer prisoners out of the facility since then, amid public and congressional pressure to close it.

The population has now dwindled to just 15 after the most recent series of transfers.

Among them is 9/11 mastermind Khalid Sheikh Mohammed, who agreed to plead guilty after negotiations with military lawyers, avoiding a potential death sentence, and setting off yet another legal saga. 

Trump himself ordered his then-Defense Secretary Jim Mattis to keep Guantanamo open in 2018, reversing an Obama administration order.