After 9/11, 'we tortured some folks: Obama

President Barack Obama has acknowledged that US officials had "tortured some folks" in the aftermath of the September 11, 2001 attacks, but urged they not be judged too harshly.

The US administration is expected to release a declassified Senate report in the coming days that will detail abuses by intelligence agents targeting extremist groups in the wake of the attacks.

"Even before I came into office, I was very clear that in the immediate aftermath of 9/11, we did some things that were wrong," Obama told reporters on Friday.

"We did a whole lot of things that were right, but we tortured some folks. We did some things that were contrary to our values."

Apparently preparing the ground for the report, Obama said intelligence personnel had been under extreme pressure in 2001 and after.

"People did not know whether more attacks were imminent and there was enormous pressure on our law enforcement and our national security teams to try to deal with this," he said.

"It's important for us not to feel too sanctimonious in retrospect about the tough job those folks had. And a lot of those folks were working hard and under enormous pressure, and are real patriots.

"But having said all that, we did some things that were wrong, and that's what that report reflects," he added.

"And my hope is that this report reminds us once again that, you know, the character of our country has to be measured in part not by what we do when things are easy, but what we do when things are hard."

The Central Intelligence Agency has long faced allegations that its "enhanced interrogation techniques", used between 2002 and 2006 as it hunted al-Qaeda operatives, amounted to illegal rights abuses.

The Senate probe has also generated a side scandal of its own, following CIA chief John Brennan's admission this week that his officers improperly penetrated the computers of congressional investigators.

Brennan has faced calls for his resignation, but Obama said that he retained "full confidence" in him.