President Barack Obama on Tuesday presented a long-awaited roadmap to close the controversial US military prison at Guantanamo Bay, saying it was time to shutter a facility that betrayed US interests and values.

With less than a year left in office, Obama unveiled a plan that says the US should continue to transfer low-risk detainees to other countries and which describes how 13 possible replacement facilities could save the US taxpayer millions of dollars each year.

"For many years, it's been clear that the detention facility at Guantanamo Bay does not advance our national security. It undermines it," Obama said in a White House address.

"This is about closing a chapter in our history. It reflects the lessons that we've learned since 9/11 - lessons that need to guide our nation going forward."

A total of 91 suspected jihadists remain at Guantanamo, a prison that once housed about 700 inmates at its peak and has become synonymous around the world with torture, indefinite detention and orange jumpsuits.

Obama has pushed for Guantanamo's closure since taking office in 2009, but his efforts have been thwarted by Republican lawmakers, many of whom see it as a useful tool in combating terror. Obama says the opposite is true, and that the facility feeds into anti-US, jihadist propaganda.

The US president also has faced opposition from within his own administration, with the Pentagon accused of slow-pedaling transfers and overstating closure costs.

"This plan deserves a fair hearing, even in an election year," Obama said on Tuesday.

'Dangerous precedent'  

The Guantanamo Bay closure plan, which took months to produce, gives few specifics on where a US facility would be, but military officials have previously listed Fort Leavenworth, Kansas or the US Navy brig in Charleston, South Carolina among the possible destinations for inmates.

Those locations, however, face objections from local politicians.

The US leader has long argued that many Guantanamo prisoners should be transferred overseas and some should be tried by military courts.

The Guantanamo Bay prison once had 700 inmates.

A small number - those deemed too dangerous to release but too difficult to prosecute - would be held in the US.

But Congress has placed a ban on transfers to the US, deepening the legal thicket.

Human rights groups worry this would only extend detentions without trial and create a "Guantanamo North."

"The possibility of a new, parallel system of lifelong incarceration inside the US without charge would set a dangerous precedent," Amnesty International said in a statement.

"If successfully mounted, it would be a devastating blow to basic principles of criminal justice."

Saving money?  

The plan says a US facility would save money over time. It currently costs about $455mn each year to run Guantanamo, and a US site would reduce that amount by up to $180mn.

Most of the savings would come from a decrease in the number of troops guarding the reduced population on the US mainland, but it could cost as much as $475mn in one-time expenses to move the men and build or update a facility to hold them.

"However, within three to five years the lower operating costs of a US facility with fewer detainees ... could fully offset these transition costs," the report notes.

91 prisoners left  

Both as a candidate and while president, Obama promised to close Guantanamo, arguing indefinite detention and "enhanced interrogation" violated the nation's values and handed militants a potent recruiting tool.

Efforts to transfer prisoners overseas have been stymied by unrest in Yemen - a likely destination for many - and by recidivism among those already released.

Still, Defense Secretary Ashton Carter has in recent weeks signed off on a flurry of transfers, and last month, the prison's population dropped below 100 for the first time.

Today, 91 inmates remain. Of them, 35 have been approved for release. The rest face ongoing, indefinite detention.

Perhaps the most notorious prisoner is Khalid Sheikh Mohammed, who along with four co-defendants is charged with plotting the September 11, 2001 attacks.

The Guantanamo Bay military prison was opened in January 2002 on a US naval base on a coastal spit of land in southeastern Cuba, leased from Havana under a treaty dating back to 1903.

It was set up after the 9/11 attacks under the administration of then-president George W. Bush to deal with prisoners who were termed "enemy combatants" and denied many US legal rights.