US President Barack Obama has pledged to make a new push to close the Guantanamao detention camp.

He said his administration would re-engage with Congress in an attempt to overcome obstacles to shutting the facility.

"It needs to be closed," Mr Obama told a White House news conference. "I'm going to go back at this."

But he offered no new path to removing congressional, political and legal hurdles he faces.

Mr Obama failed to make good on his promise to close the prison at the US military base in Cuba.

It was opened by his predecessor George W Bush to house foreign terrorism suspects, within a year of taking office in early 2009.

Meanwhile, the American Medical Association has questioned whether doctors are being asked to violate their ethics by force-feeding prisoners on hunger strike at the Guantanamo detention camp.

The US Navy has sent extra medical personnel to the camp because of the growing protest.

The reinforcements arrived at the weekend and included about 40 nurses, specialists and hospital corpsmen, who are trained to provide basic medical care.

One hundred of the 166 detainees had joined a hunger strike that began in February to protest their continued detention at  Guantanamo Bay.

A spokesman said 21 of those had lost enough weight that they were being fed liquid supplements via tubes inserted in their noses and down into their stomachs.

Five were in the hospital for observation but did not have life-threatening conditions.

Last Thursday, the AMA president, Dr Jeremy Lazarus, sent a letter to US Defense Secretary Chuck Hagel reiterating its long-held position that it is a violation of medical ethics to force-feed mentally competent adults who refuse food and life-saving treatment.

The letter stopped short of asking Mr Hagel to halt force-feedings at Guantanamo.

It urged Mr Hagel "to address any situation in which a physician may be asked to violate the ethical standards of his or her profession".

Mr Hagel had just returned from a trip to the Middle East and it was unclear whether he had seen the letter, a Pentagon spokesman said.

Asked if military doctors had raised ethical concerns about being asked to perform force-feedings, the spokesman said: "I can tell you there have been no organised efforts, but I cannot speak for individual physicians.

"I can tell you that we will not allow detainees to harm themselves, and this includes attempts at suicide - including self-induced and peer-pressured starvation to death," he added.

The military has said that some prisoners are pressuring others to join the hunger strike, and that some of those being tube-fed occasionally eat regular meals or voluntarily drink nutritional supplements when they are removed from their cell blocks and are alone with medical personnel.