Media playback is unsupported on your device Media caption President Obama: "Guantanamo is not necessary to keep America safe... it is a recruitment tool for extremists; it needs to be closed"

US President Barack Obama has pledged a new push to close the prison at Guantanamo Bay, Cuba, amid a growing prisoner hunger strike there.

At the White House, Mr Obama said the detention centre was "contrary to who we are" and harmful to US interests.

He cited recent convictions of terror suspects to argue the civilian justice system was adequate for such trials.

Congress has blocked efforts to close the prison, but Mr Obama said he would renew discussions with lawmakers.

Mr Obama told reporters he had asked a team of officials to review operations at Guantanamo Bay and said he was not surprised there were problems there.

"It is inefficient, it hurts us in terms of our international standing, it lessens co-operation with our allies on counter-terrorism efforts, it is a recruitment tool for extremists, it needs to be closed," Mr Obama said.

'No longer necessary'

He described the detention facility at Guantanamo Bay as a "lingering problem" that would worsen if it remained open.

"I think it is critical for us to understand that Guantanamo is not necessary to keep America safe," Mr Obama told reporters.

Media playback is unsupported on your device Media caption The BBC's Jonathan Beale said there are no signs the prison camp will be closed down

He said that with the war in Iraq over and detention authority in Afghanistan transferred to Afghan forces, the facility in Cuba was no longer necessary.

Mr Obama said he would need the help of Congress to devise a long-term legal solution to the prosecution of detainees.

The president's comments come amid a hunger strike that has spread in recent weeks to include more than 100 of the 166 inmates at the facility.

They are protesting against their indefinite detention. Most are being held without charge.

UN Human Rights Commissioner Navi Pillay has said Guantanamo Bay should be shut immediately.

The UN has called the continued detention of so many people without trial a clear violation of international law, though it understands Congress has blocked Mr Obama from closing the prison, the BBC's Imogen Foulkes says in Geneva.

Aid agencies are convinced the situation there cannot go on. The International Committee of the Red Cross, the only agency with access to individual detainees, says there is now an unprecedented level of desperation at Guantanamo, our correspondent adds.

Image caption A medical officer at Guantanamo holds a feeding tube in 2007

On Tuesday, a UN spokesman said the force-feeding of prisoners was also a probable human rights violation.

"If it's clearly against the will of the people who are being forcibly fed, then in a view of the World Medical Association and indeed our view, this would amount to cruel, inhumane and degrading treatment which is not permissible under international law," said Rupert Colville, the UN spokesman on human rights.

In his remarks, the president seemed to support the US practice of force-feeding some hunger-strikers.

"I don't want these individuals to die," he said. "Obviously the Pentagon is trying to manage the situation as best we can."

The US has had to reinforce medical staff at Guantanamo Bay, with about 40 nurses and other specialists arriving at the weekend, according to a camp spokesman.

Cleared for release

The strike began in February but spread in recent weeks to include more than 100 of the 166 people held at the facility.

Media playback is unsupported on your device Media caption Two commentators joust on whether Guantanamo should be shut

Guantanamo officials deny claims that the strike began after copies of the Koran were mishandled during searches of prisoners' cells.

A spokesman for the detention camp told Reuters news agency that 21 prisoners were being force-fed through tubes inserted through their noses, while five had been brought to hospital for observation but did not have life-threatening conditions.

Shorter hunger strikes have happened at Guantanamo since early 2002, when the US began bringing al-Qaeda and Taliban prisoners there.

Violence erupted at the prison on 13 April as the authorities moved inmates out of communal cellblocks where they had covered surveillance cameras and windows.

Some prisoners used "improvised weapons" and were met with "less-than-lethal rounds", camp officials said, but no serious injuries were reported.

Nearly 100 of the detainees have reportedly been cleared for release but remain at the facility because of restrictions imposed by Congress as well as concerns of possible mistreatment if they are sent back to their home countries.

Senator Dianne Feinstein, the chair of the Senate Intelligence Committee, wrote to National Security Council Director Tom Donilon last week asking for the administration to "renew its efforts" to transfer the cleared prisoners.

Sen Feinstein and another committee member had earlier asked the Obama administration to temporarily halt the transfer of 56 cleared Yemeni nationals after an attempted bombing claimed by al-Qaeda in Yemen in December 2009.

Soon after his election, Mr Obama made closing Guantanamo Bay a top priority for his new administration, pledging to close it within a year of his inauguration in January 2009.

But his plan to transfer prisoners to maximum security prisons in the US and try some detainees in the civilian justice system met fierce resistance from lawmakers of both parties.