Barack Obama branded the original military trials an enormous failure
President Barack Obama has announced he is to revive military trials for some detainees at Guantanamo Bay.
However, in a statement he said legal rights for those facing the military commissions would be improved.
Mr Obama had halted the trials as one of his first acts on taking office in January, saying the US was entering a new era of respecting human rights.
The decision to revive the military trials has brought harsh criticism from some US civil liberties groups.
There are currently 240 detainees still at the US base in Guantanamo Bay, Cuba.
On the campaign trail last year, Mr Obama had branded the military commissions "an enormous failure".
However, analysts say that although Mr Obama has condemned the Military Commissions Act, set up by his predecessor George W Bush, he has never ruled out revamping it.
In the statement issued on Friday, the US president said military commissions were appropriate for trying enemies who violate the laws of war, provided that they are properly structured and administered.
But he said he had opposed the tribunals used by the Bush administration because they had failed to establish a legitimate legal framework and undermined swift and certain justice.
The improved rights for detainees include restrictions on hearsay evidence; a ban on evidence obtained by cruel treatment; giving detainees more leeway to choose their own lawyers; and protecting detainees who refuse to testify, the statement said.
Mr Obama said he is seeking more time so that the new procedures can be implemented.
"These reforms will begin to restore the commissions as a legitimate forum for prosecution, while bringing them in line with the rule of law," Mr Obama said.
"This is the best way to protect our country, while upholding our deeply held values."
Earlier, as White House aides released details of Mr Obama's impending statement, rights groups reacted with dismay.
Zachary Katznelson of Reprieve, which represents a number of Guantanamo Bay detainees, told the BBC that the president was making a "fundamental mistake".
"He is taking a gravely, truly flawed system, tinkering at the edges and hoping that the world is somehow going to see this as legitimate, as open, as fair - it's not going to happen," he said.
"There is no way that these trials should be rehabilitated. We should move people to the civilian courts. It's tried, it's tested, it works."
The BBC's James Coomerasamy, in Washington, says that although some are disappointed, for others it is further evidence of Mr Obama's pragmatic style of leadership, one that recognises the need to balance the change he has promised with the reality he has inherited.
Shortly before Mr Obama's announcement, US officials said that Algerian detainee Lakhdar Boumediene had left Guantanamo Bay for France.
Mr Boumediene was arrested in Bosnia in 2001 and was held for seven years. He was cleared of any wrongdoing in November.