The White House gave explicit written approval to the waterboarding of captured al-Qaida suspects by their CIA interrogators, it was reported today.

The report in today's Washington Post presents the most compelling evidence to date that the highest levels of George Bush's White House gave approval to the specifics of an interrogation practice in which detainees were strapped to a board while water was poured down their nose and throats.

Two secret memos were issued at the CIA's request, in 2003 and 2004, to authorise waterboarding.

The then director of the CIA, George Tenet, had asked for the written authorisation because he was worried about a possible backlash – including possible prosecution - of intelligence officials, the Post reported.

"The suggestion that someone from [the] CIA came in and browbeat everybody is ridiculous," one former agency official told the Post.

"The CIA understood that it was controversial and would be widely criticised if it became public. But given the tenor of the times and the belief that more attacks were coming, they felt they had to do what they could to stop the attack."

The existence of the memos provides the first clear evidence that the White House was involved in the specifics of how al-Qaida suspects were interrogated.

Until today, it was known only that the White House had given sweeping approval to kill or capture al-Qaida operatives in George Bush's memo authorising the war on terror on September 15 2001.

But it was not known how deeply the White House had involved itself in the treatment of detainees.

Civil rights organisations today said the report provided new evidence of the close involvement of the White House in establishing a standard of treatment for detainees that was put in operation from Guantanamo to Abu Ghraib.

"This new report supplies further evidence that the decision to endorse torture was made by the administration's most senior officials," Jameel Jaffer, a lawyer for the American Civil Liberties Union, said in a statement.

The newspaper did not specify who signed the memos, or provide detailed accounts of their contents.

However, its account of the exchanges over time between a worried Tenet and the White House suggest that the CIA director was anxious for the Bush administration to sign off on waterboarding at the highest possible levels.

By 2003, when the White House issued the first memo described today by the Post, at least three high level al-Qaida suspects had already been subjected to waterboarding, including Khalid Sheikh Mohammed, the mastermind of the 9/11 attacks.

By that point as well, US justice department officials had already provided the CIA with legal cover for the technique in a 2002 memo.

But apparently the justice department approval was not reassurance enough for the CIA, which was concerned at creating a paper trail showing the Bush administration had authorised the practice.

The White House issued its first memo in June 2003 following a meeting between Tenet and members of the national security council, the Post reported.

Condoleezza Rice, the then national security adviser, attended the meeting.

A few days later, the White House issued a brief memo authorising the CIA's interrogation method.

Those concerns grew deeper in April 2004 when the revelations about the mistreatment and humiliation of detainees at Abu Ghraib prison became an international scandal. Tenet made a request for additional authorisation in June 2004. The authorisation came in mid-July.

The first indication that the White House had direct knowledge of specific interrogation techniques came to light last month during extraordinary testimony to Congress by Condoleezza Rice, who was national security adviser during Bush's first term.

In written testimony, Rice told Congress that she and other senior
officials, including the vice-president, Dick Cheney, had been briefed by Tenet about waterboarding in early 2002.

Rice said officials were so concerned about the use of such tactics that they directed the justice department to investigate whether they were legal.