US authorities plan to hold long-deferred hearings for dozens of detainees held at Guantanamo to decide if they still pose a threat to the United States, the Pentagon said Monday.

President Barack Obama had ordered the review boards back in March, 2011 but it has taken more than two years for US government agencies to finally carry out the plan, with rights groups criticizing the administration for the delay.

The announcement follows renewed pledges from Obama to close the controversial Guantanamo jail, despite opposition from some members of Congress, and comes against the backdrop of a hunger strike by dozens of detainees.

The review hearings will apply to 71 of the 166 men held at the prison at the US naval base in Guantanamo Bay, Cuba, spokesman Lieutenant Colonel Todd Breasseale said.

Most of that group have been designated as too dangerous to release but have not been charged with any crime as there is not enough permissible evidence to allow a trial.

Rights advocates have long urged the review panels to be established and Human Rights First praised the move.

"Though long-delayed, this is a welcome step forward toward fulfilling the president's promise to shutter the US detention facility at Guantanamo," Daphne Eviatar of Human Rights First said in a statement.

She called on the administration to ensure detainees are allowed to have a lawyer and that the proceedings be open to outside observers.

The "periodic review boards" will not examine whether the detainees are being held lawfully at Guantanamo, but only whether the inmates still constitute a security threat to America that merits continued detention, Breasseale said in a statement.

The boards will "determine whether continued detention is warranted for certain detainees to protect against a continuing significant threat to the security of the United States," he said.

In each case before the board there will be a "hearing, at which the detainee or his representatives will be able to present information and argument in his favor," he said.

The Pentagon has begun notifying detainees about the boards but officials did not say when the panels would start holding hearings or whether journalists would be allowed to follow the proceedings.

"No boards have yet convened and will only begin once all the reasonable conditions have been set," Breasseale said.

He added that the number of detainees to appear before the reviews boards is "subject to change."

The new boards will include senior officials from the departments of Defense, Justice, State and Homeland Security, as well as intelligence officials and officers from the US military's Joint Staff.

Authorities at Guantanamo previously had held reviews, called combat status review trial hearings, that assessed if a detainee was correctly identified and whether he qualified as an "enemy combatant."

But the planned hearings announced by the Pentagon are a new step, allowing detainees to argue against accusations that labeled them a security threat.

In the wake of the US-led invasion of Afghanistan following the September 11, 2001 attacks, Washington opened the Guantanamo prison to hold suspected militants captured on the battlefield by American forces or handed over by other governments.

More than half of the detainees have been cleared for release and face no charges in the United States. Most of them are Yemenis detained years ago but US authorities had feared they would be recruited to extremist groups if returned to their home country.

As part of his renewed bid to shutter the prison, Obama has promised to lift a moratorium on transferring the Yemeni detainees back to their homeland.