President Barack Obama brought back Bush-era military trials for terror suspects at Guantanamo Bay by signing into law new rules that will give detainees stronger legal rights in court.
Obama approved the rules, most of which he proposed in May, as part of a $ 680 billion defence policy bill that cut some pricey and overlapping military weapons programs.
Obama did not mention Guantanamo during the short White House ceremony.
More than 220 detainees remain at Guantanamo as the Obama administration decides how to prosecute some in US courts and turns over others to nations that are willing to rehabilitate or free them.
Additionally, the administration is grappling with how to keep in prison a small handful of remaining detainees who are considered too dangerous to release or put on trial.
The new rules for military commissions replace a system for Guantanamo trials that was put in place during the administration of former President George W Bush.
The old system limited detainees' legal rights to defend themselves at trial, in part by allowing the use of hearsay and coerced statements to be used against them.
Civil rights and constitutional law advocates said the changes that they called improvements still fell far short of guaranteeing detainees' rights.