"Two Saudis and one Yemeni, each located in Camp 1, were found unresponsive and not breathing in their cells by guards," U.S. Southern Command said in a statement.

The military said attempts to resuscitate the detainees failed and they were pronounced dead by a physician at Guantanamo, which holds just under 500 foreigners captured mainly in the U.S. war against the Taliban in Afghanistan.

Facing indefinite detention with none of the rights afforded formal prisoners of war, or criminal suspects in the U.S. justice system, dozens of the detainees have undertaken hunger strikes.

Several have also attempted suicide while at least one fake suicide attempt was staged recently to trick prison guards into going into a cell where detainees intended to ambush them.

The names of the deceased -- the first deaths at Guantanamo since it started being used as a prison camp in 2002 -- were not released.

The U.S. military said the bodies were being treated "with the utmost respect." An investigation had begun, it said.

The United States has faced criticism from human rights groups and some of its allies for indefinitely holding prisoners at Guantanamo. President George W. Bush has said he would like to close the detention center.