US military guards walk within Camp Delta military-run prison at the Guantanamo Bay naval base in Cuba. (AP/Brennan Linsley)

US senators have showed their paralysis over what to do with the Guantanamo Bay prison, voting down duelling bills to loosen and tighten restrictions on transferring detainees.

Nearly 12 years after its creation and almost five years since President Barack Obama vowed on his first day in office to close the prison, 164 suspects remain at the US naval base in Cuba. Restrictions imposed by Congress have brought transfers to a virtual standstill, even though more than half the men there have been cleared for transfer.

An amendment to the Senate's annual defence policy bill proposed by senators Carl Levin and John McCain would have eased the Obama administration's ability to detain and try suspects in the United States or release them overseas. But it fell eight votes shy of the 60-vote threshold needed for passage. The vote was 52-46.

Mr McCain read a letter from 38 former US military leaders voicing their support. The letter called Guantanamo a "symbol of torture" and a recruiting tool for al Qaida.

Earlier, an opposing amendment championed by Republican senators that would have made it even harder for Mr Obama to move prisoners was defeated 55-43.

One of the backers, Senator James Inhofe, defended the treatment of Guantanamo detainees and said one of their biggest problems was obesity. "They're eating better than they've ever eaten at any other time in their life," he said.

The stalemate leaves language in the defence bill that only slightly advances Mr Obama's cause. The White House has called the bill constructive while insisting that more be done to provide officials with the necessary flexibility to close the prison.

Any final law needs the Republican-led House of Representatives' support, and such a scenario is highly unlikely.

Mr Obama's effort to loosen restrictions on Guantanamo detainees faces dogged resistance, with opponents citing the cases of some suspects who have been released to foreign countries only to later join terrorist efforts.

Earlier this year, the lower house banned sending detainees to Yemen, where more than half the remaining detainees come from. Yemen is also home to perhaps al Qaida's most active branch.

Mr Obama established his own ban on Yemeni transfers after a Nigerian man tried to blow up a US-bound flight four years ago with explosives hidden in his underwear. The bombing instructions came from al Qaida operatives in Yemen.

Mr Obama lifted the moratorium in May, calling Guantanamo a "symbol around the world for an America that flouts the rule of law".

Senate advocates of closing Guantanamo repeatedly cited the high cost of maintaining the jail - 2.7 million dollars (£1.6m) a year per prisoner.

Total spending on Guantanamo amounts to 454 million dollars (£282m) a year, according to the Defence Department.

AP