US President Donald Trump has signed an executive order to keep Guantanamo Bay military prison open.
Mr Trump announced the move in his State of the Union address.
The decision reverses that of former President Barack Obama, who had said he wanted to close the controversial site "as soon as practicable".
The facility in Cuba has been used since the 9/11 attacks to detain what Washington calls "enemy combatants", but only 41 prisoners remain there.
Hundreds were transferred away from the facility during the Obama era.
A White House statement confirmed the order had been signed to resist the detention facility's closure, and affirmed the administration's right to detain enemy combatants when necessary.
"Terrorists are not merely criminals. They are unlawful enemy combatants. And when captured overseas, they should be treated like the terrorists they are," Mr Trump said during Tuesday's speech.
"In the past, we have foolishly released hundreds of dangerous terrorists only to meet them again on the battlefield," he added, giving as an example the Islamic State group's leader Abu Bakr al-Baghdadi, who was held in US custody in Iraq.
The first detainees were sent there in January 2002, and more than 700 have been held there since - many without charge or criminal trial.
The facility has been controversial since its opening, with human rights groups complaining about conditions there amid allegations of torture.
The Obama administration signed an order in 2009 to close the site within a year, but faced eight years of tight restrictions from lawmakers on the transfers.
The reversal has been a long-standing policy for Mr Trump, who campaigned on keeping Guantanamo open, saying in 2016 he wanted to "load it up with some bad dudes".
While president-elect he tweeted that there should be "no further releases" from the facility, and in November last year he said he would consider sending a suspect in October's Manhattan truck attack which killed eight people to the prison.