U.S. authorities say they have transferred to other countries four prisoners from the U.S. military detention center at Guantanamo Bay, Cuba, in the likely final such move under the Obama administration.

The transfer reduces the prison population at the site to 41, the Pentagon said on January 19.

The Pentagon did not immediately provide further details. Saudi Arabia later said that one of the released was a Saudi citizen who had arrived in his home country on January 19.

When he took office eight years ago, U.S. President Barack Obama said his goal was to close the prison during his administration.

Obama, in his last full day in office, assailed Congress in a two-page letter for blocking his efforts to close the facility and said it never should have been built in the first place.

"There is simply no justification beyond politics for the Congress' insistence on keeping the facility open," Obama wrote.

Donald Trump, who will assume the presidency on January 20, has called for the prisoner transfers to stop and vowed to increase the number of terror suspects held there.

Based on reporting by Reuters and AFP