Washington - President Barack Obama on Thursday released four internal legal opinions that were used by former president George W Bush's administration as justification for harsh CIA interrogations, but ruled out prosecuting anyone involved in such practices.

The memorandums released by the Justice Department offered legal justification for a series of harsh interrogation tactics against suspects held in CIA prisons, including sleep deprivation and a drowning-simulation technique known as waterboarding, which some human rights groups have said amounted to torture.

But Obama said he had no intention to prosecute any CIA officials involved in the interrogations.

"In one of my very first acts as president, I prohibited the use of these interrogation techniques because they undermine our moral authority and do not make us safer," Obama said in a statement.

"In releasing these memos, it is our intention to assure those who carried out their duties relying in good faith upon legal advice from the Department of Justice that they will not be subject to prosecution," Obama said.

Civil rights group ACLU welcomed the release but said it was still pushing for an independent prosecutor to investigate allegations of torture under the Bush administration.

"We have to look back before we can more forward as a nation," said Anthony Romero, executive director of the ACLU. "When crimes have been committed, the American legal system demands accountability." (dpa)