Three of the five detainees were from Yemen, one was from Somalia, and the fifth from Kenya.

They have spent a collective 85 years in the prison opened two decades ago for so-called "war on terror" detainees in the wake of the September 11, 2001 Al Qaeda attack on the United States.

Never charged, detainees now approved for release -- decided after case reviews in November and December -- total 18 of the 39 men still held in the prison facility at the US Naval Base in Cuba.

Those newly approved for release are Somali Guleed Hassan Ahmed, (also called Guled Hassan Duran); Kenyan Mohammed Abdul Malik Bajabu; and Omar Muhammad Ali al-Rammah, Moath Hamza al-Alwi, and Suhayl al-Sharabi of Yemen.

The Pentagon's Periodic Review Board found that all did not present, or no longer presented, a threat to the United States.

But like the others approved, their releases could be delayed as Washington seeks arrangements with their own or other countries to accept them.

Currently the United States will not repatriate Yemenis due to the civil war in that country, or Somalis, whose homeland is also mired by domestic conflict.

The release approvals indicated an accelerated effort by the administration of President Joe Biden to resolve the situations of the 39 in Guantanamo, after his predecessor Donald Trump effectively froze action.

Tuesday marked the 20th anniversary of the opening of the Guantanamo prison, and brought calls from international human rights groups to shut it down.

Of the 39, 10 are in the process of standing trial, mostly still in preliminary proceedings; two have pleaded guilty to terror-related charges; and nine remain in limbo, neither charged nor yet granted release.