Riyadh: Relatives of two Saudi detainees who died at Guantanamo Bay said the men could not have committed suicide as the US military reported, because they were strict Muslims, newspapers reported on Monday.

Islam prohibits suicide and sets out harsh punishments in the after-life for those who take their own lives. The men's families said they had probably been killed.

"I am confident my son did not commit suicide," Talal Al Zahrani, Yasser's father, told Asharq Al Awsat newspaper.

"The story of the US administration is a lie."

Zahrani's brother, Ahmed, also said it was unthinkable that Yasser would kill himself.

"It's impossible for Yasser to commit suicide," he told Al Watan newspaper.

"He was killed," said another brother, Abdullah.

Fares Al Otaibi, Manei's brother, also suspected foul play.

"We are 100 per cent suspicious about his death," he told the newspaper.

The two Saudis and one Yemeni were the first prisoners the US military has reported as dying at the base in Guantanamo, where the United States has held "terrorism" suspects since 2002.

Washington said they hanged themselves with clothes and bedsheets.

The deaths renewed criticism of the base, which many human rights groups say should be closed.

Nearly all the prisoners at Guantanamo are being held without charge and some have been held for more than four years.

The US military camp holds 460 foreigners captured mainly in Afghanistan during the US-led war there to oust the Taliban and Al Qaida after the 9/11 attacks.

There have been many previous suicide attempts at Guantanamo. Before Saturday, 23 prisoners had tried to kill themselves in 41 suicide attempts.