Extra medical staff have been sent to the US military prison in Guantanamo Bay to help address a hunger strike that has spread to nearly two-thirds of the detainees.

Some 40 US Navy medical personnel, including nurses and specialists, arrived over the weekend, said on Monday Lieutenant Colonel Samuel House, a military spokesman at Guantanamo.

"The influx of personnel was planned several weeks ago as increasing numbers of detainees chose to protest their detention," he said.

With the strike now entering its 12th week, President Barack Obama has faced fresh calls to honour his promise to close the prison at the US base in Cuba, which holds 166 individuals captured as part of the "War on Terror."

House said 100 of the 166 inmates are striking, a number that has not changed since Saturday. Of those, 21 are receiving feeding through nasal tubes, the spokesman said, one more than on Saturday.

Growing anger

Five are hospitalised, he added in the statement, without specifying whether any were in life-threatening condition.

Lawyers for the detainees have said around 130 inmates are observing the hunger strike, more than officially acknowledged.

The rapidly growing protest movement began on February 6, when inmates claimed prison officials searched Korans in a way they considered blasphemous, according to their lawyers.

Officials have denied any mishandling of Islam's holy book.

But the strike has now turned into a larger protest by prisoners against their indefinite incarceration without charge or trial over the past 11 years.

Calls for closure

More and more critics have called for the immediate closure of the facility.

Among them is former chief prosecutor at Guantanamo, Air Force colonel Morris Davis, who warned that "unless President Obama acts soon, I believe it is likely one or more of the detainees will die."

Andrea Prasow, senior counterterrorism counsel and advocate at Human Rights Watch, said "there has never been such a critical moment in the history of Guantanamo."

Senator Dianne Feinstein, a Democrat from California, wrote a letter to Obama asking the administration to "renew its efforts" to transfer out the 86 detainees who were cleared for such a move by US military authorities.

She also called for the reassessment of the "security situation on the ground in Yemen, because is my understanding that 56 of the 86 detainees cleared for transfer are Yemeni."

Obama imposed a moratorium on repatriating Yemenis held at Guantanamo in 2009 after a plot to blow up an airliner on Christmas Day was traced back to Al-Qaeda's Yemeni franchise.

Source: Agencies