WASHINGTON: Saying it was damaging to U.S. interests to keep holding prisoners in legal limbo at Guantanamo, President Barack Obama renewed an old vow on Tuesday to close the camp, where about 100 inmates are on hunger strike to protest against their years in detention without trial.

Human rights groups welcomed Obama's recommitment to shutting the prison. But some activists called for action, not just words, and said the president could take some steps on his own without hitting congressional obstacles.

“It's not sustainable - I mean, the notion that we're going to continue to keep over 100 individuals in a no-man's land in perpetuity,” Obama said.

Obama lamented the status quo, which has kept most prisoners in detention without trial or charge since the prison was set up at the US Naval Base on Cuba in 2002 to hold foreign terrorism suspects.

A renewed effort to close the camp would mean finding a series of solutions - some of which would likely come up against the same congressional opposition they faced in the past given lawmakers' reluctance to have inmates transferred to the United States.

Obama, who repeatedly pledged to close the camp when he was campaigning for a first term and after he first took office in 2009, put the blame on Congress for his failure to make good on his promise and said he would re-engage with lawmakers on the issue.

While Obama acknowledged an uphill fight and provided few specifics on how to overcome legal and political obstacles, White House spokeswoman Caitlin Hayden later said he was weighing a range of options aimed at reducing the number of inmates and moving toward “ultimate closure.”

She said Obama could implement some measures on his own, including naming a new senior State Department officer to refocus on repatriating detainees or transferring them to third countries, a process that has ground to a halt. That post has been vacant since January.

“We will also work to fully implement the Periodic Review Board process, which we acknowledge has not moved forward quickly enough,” she said. This is a system of parole-style hearings the Obama administration set up but which have left many inmates frustrated over the slow handling of their cases.

Obama's comments were his first public remarks about Guantanamo since the hunger strike began in early February.

Military officials have attributed the protest in part to a sense of hopelessness among detainees over their open-ended detention.

Long a subject of international condemnation but low on the list of the American public's policy concerns, Guantanamo has been thrust back in the spotlight by the hunger strike and the military's decision to force-feed prisoners to keep them alive.

The US military has said 21 prisoners are being force-fed liquid meals through tubes inserted in their noses. Forty medical personnel have been sent to reinforce the military's existing teams at Guantanamo to deal with the hunger strike.