Three detainees at the US base at Guantanamo Bay, Cuba have died in what appears to have been a suicide pact.
These are the first suicides at the base, despite dozens of attempts
The inmates, two Saudis and a Yemeni, hanged themselves in their cells.
The camp commander said the deaths - the first at the camp - were planned in "an act of warfare". Rights groups said they were driven by despair.
President George Bush expressed "serious concern" over the suicides at Guantanamo, which holds about 460 men captured in the US "war on terror".
There have been dozens of suicide attempts since the camp was set up four years ago - but none successful until now.
The men were found unresponsive and not breathing by guards on Saturday morning, said officials.
They were in separate cells in Camp One, the highest security section of the prison.
They hanged themselves with clothing and bed sheets, camp commander Rear Adm Harry Harris said.
He said medical teams had tried to revive the men, but all three were pronounced dead.
A military investigation into the deaths is now under way.
Rear Adm Harris said he did not believe the men had killed themselves out of despair.
"They are smart. They are creative, they are committed," he said, quoted by Reuters.
"They have no regard for life, either ours or their own. I believe this was not an act of desperation, but an act of asymmetrical warfare waged against us."
All three men had previously taken part in some of the mass on-and-off hunger strikes undertaken by detainees since last August, reported news agency Reuters, and all three had been force-fed by camp authorities.
The agency said all three had left suicide notes, but that no details had been made available.
White House spokesman Tony Snow said Mr Bush "expressed serious concern" at the deaths.
"He also stressed that it was important to treat the bodies humanely and with cultural sensitivity," he said.
A spokesman for UK Prime Minister Tony Blair described the suicide as a "sad incident".
Mr Blair has in the past described Guantanamo as "an anomaly that has to end".
The deaths will increase pressure on the US from human rights groups and several European countries who have been calling for Guantanamo to be closed, says the BBC's James Westhead in Washington.
There was a chorus of protest human rights groups at the suicides, including from Amnesty International, which repeated demands for the camp to be closed.
William Goodman from the New York-based Centre for Constitutional Rights told AFP news agency the men were "heroes for those of us who believe in basic American values of justice, fairness and democracy"
Mr Goodman, whose organisation represents some 300 detainees, said the government had denied them that.
Ken Roth, head of Human Rights Watch in New York, told the BBC the men had probably been driven by despair.
"These people are despairing because they are being held lawlessly," he said.
"There's no end in sight. They're not being brought before any independent judges. They're not being charged and convicted for any crime."
On Friday, President Bush said he would "like to end Guantanamo".
"There are some that, if put out on the streets, would create grave harm to American citizens and other citizens of the world. And, therefore, I believe they ought to be tried in courts here in the United States," he added.