Mr Obama is facing domestic opposition to his plan to close the camp
A Yemeni inmate at the Guantanamo Bay prison camp has died in an apparent suicide, US military officials say.
The man, named as Muhammad Ahmad Abdallah Salih, becomes the fifth person believed to have killed himself at the facility in Cuba.
He had been held there without charge since 2002 and was thought to have been taking part in a hunger strike.
US President Barack Obama wants to close the camp by January 2010, but is facing considerable opposition.
The US accused the man, who was also known as Al Hanashi, of fighting with the Taliban in Afghanistan.
The military said he was found unresponsive and not breathing in his cell by prison guards.
In a statement, it said "extensive lifesaving procedures" were carried out before he was pronounced dead.
Mr Obama wants to shut down the controversial camp, but Congress recently rejected his request for money to help with the process.
A new opinion poll has also suggested that a majority of Americans now oppose Guantanamo's closure.
But Guantanamo critics said the Yemeni inmate's death emphasised the need to act as soon as possible.
"This kind of desperation is caused by the uncertainty of not knowing whether one will ever be released or even charged," the Associated Press quoted Ben Wizner, an American Civil Liberties Union lawyer, as saying.
About 240 detainees remain at the camp.