Dick Cheney, the former vice president, ordered a highly classified CIA operation hidden from Congress because it pushed the limits of legality by planning to assassinate al-Qaida operatives in friendly countries without the knowledge of their governments, according to former intelligence officials.

Former counter-terrorism officials who retain close links to the intelligence community say that the hidden operation involved plans by the CIA and the military to launch operations, similar to those by Israel's Mossad intelligence service, to hunt down and kill al-Qaida activists abroad without informing the governments concerned, even though some were regarded as friendly if unreliable.

The CIA apparently did not put the plan in to operation but the US military did, carrying out several assassinations including one in Kenya that proved to be a severe embarrassment and helped lead to the quashing of the programme.

A former intelligence official said the plan was hatched in the cauldron of the September 11 attacks when officials were pushing various forms of unilateral action and some settled on the Israelis as an example.

"One of the most sensitive areas has been what we do in friendly countries that don't want to co-operate or maybe we don't have enough confidence to entrust them with information. If you have an al-Qaida guy wandering around certain bits of the world we might decide that we need to deal with that ourselves, directly, without making a lot of noise," he said. "There was a plan to deal with that. It was much talked about in the CIA and the military had its own operation."

Another former senior intelligence official responsible for dealing with al-Qaida said that assassination plans were reined in after similar covert operations by the military were botched and proved to be embarrassing, particularly the killing in Kenya. He did not give details of the operation.

The official said he believes from conversations with serving members of the CIA that the area of real concern in Congress is that the planned operations may also have involved the covert surveillance of American citizens.

There appears to be common agreement among knowledgeable former intelligence officials that the controversy goes beyond the immediate question of assassination and capture of al-Qaida operatives as there have been numerous killings and detentions since the 9/11 attacks.

One former official said that the Bush administration discussed assassinations in the context of a ban introduced in the 1970s that responded to several failed CIA attempts to murder Fidel Castro, and concluded that as the US had declared itself at war with al-Qaida and the Taliban, this ban did not apply.

Peter Bergen, a senior security analyst at the New America Foundation, said that the secret operation must have gone further than that to have created such a backlash in Congress: "If it's an assassination programme of al-Qaida leaders that is hardly surprising. Clinton had an assassination programme against bin Laden. There have been 27 drone missile strikes against al-Qaida alone this year."

The CIA has declined to comment and members of Congress who were finally briefed about the issue by the CIA director, Leon Panetta, last month are bound by confidentiality.

Some former intelligence officials and Republicans have attempted to portray the programme as barely getting out of the planning stages but others in the intelligence community have said it is highly unlikely that the CIA would have kept such an operation going for eight years without advancing it.

The evident anger in Congress is fuelling demands for a full blown investigation in to the CIA's failure to disclose the programme and Cheney's role in the cover up. The Senate majority whip, Dick Durbin, said the programme could have been illegal: "The executive branch of government should not create programs like these programs and keep Congress in the dark. To have a massive program that was concealed from the leaders in Congress is not only inappropriate, it could be illegal."

Anna Eshoo, a senior Democrat on the House of Representatives intelligence committee, is also calling for a probe. "We, by no means, have the full story. We don't know who gave the order. We don't know where the money came from. We don't know all the people who were involved," she told Politico. "We need a full investigation. My preference is that we hire an attorney to come in and run this, someone that is known for their prosecutorial knowledge as well as their knowledge of this particular area of the law."