Washington (AFP) - Twelve Nobel Peace Prize laureates are urging President Barack Obama to disclose the CIA's use of torture on terror suspects since the attacks of September 11, 2001.

The potential release of a long-delayed Senate report about this "dark period" of American history has brought the country to a "crossroads," the Nobel laureates wrote in an open letter to Obama posted on the website TheCommunity.com.

Obama, who won a Peace Prize himself in 2009, recognized in very direct terms in August that the United States had engaged in torture.

"We tortured some folks," he said at the time.

But the White House is engaged in tough negotiations with lawmakers over how much of the report on CIA torture should be declassified, with the intelligence agency insisting that agents' pseudonyms be blacked out.

"The open admission by the president of the United States that the country engaged in torture is a first step in the US coming to terms with a grim chapter in its history," the Nobel laureates wrote in their letter to Obama.

"It remains to be seen whether the United States will turn a blind eye to the effects of its actions on its own people and on the rest of the world, or if it will take the necessary steps to recover the standards on which the country was founded, and to once again adhere to the international conventions it helped to bring into being."

The laureates noted that many among them had seen the effects of torture in their own countries, or were themselves "torture survivors."

After the 2001 attacks, the CIA rounded up dozens of people suspected of having ties to Al-Qaeda and used so-called enhanced interrogation techniques on them, including sleep deprivation, simulated drowning (waterboarding) or shackling detainees in painful "stress" positions for long periods of time while naked.

When he recognized use by the CIA of torture earlier this year, Obama also stressed that he had banned the use of the enhanced interrogation methods as soon as he arrived at the White House in January 2009.

He acknowledged that there had been "enormous pressure" on law enforcement and national security in the wake of the attacks on New York's Twin Towers, the Pentagon and the crash of a plane in Pennsylvania that targeted Washington.

The letter's signatories were: Oscar Arias, who was awarded the Nobel Peace Prize in 1987, Mohamed ElBaradei (2005), Carlos Belo (1996), Leymah Gbowee (2011), John Hume (1998), F.W. De Klerk (1993), Adolfo Perez Esquivel (1980), Jose Ramos-Horta (1996), Desmond Tutu (1984), Muhammad Yunus (2006), Betty Williams (1976) and Jody Williams (1997).