US officials are to study a collection of videotapes apparently made by al-Qaeda for intelligence on the activities of the militant network.

The tapes are a "vivid illustration of what terrorism means and the threats it poses", said White House spokesman Ari Fleischer.

This is a serious reminder of the type of enemy we're up against

Ari Fleischer White House spokesman

Experts believe the tapes could provide evidence that the militants led by Osama Bin Laden are involved in the development of chemical weapons.

In another development, US media are reporting that a group with links to al-Qaeda may have experimented with the deadly toxin ricin in northern Iraq in recent months.

According to a US official who spoke on condition of anonymity, the Ansar al-Islam group tested ricin on animals and at least one human being in a part of Iraq beyond the control of Saddam Hussein.

Ricin is a biological agent which can kill by inhibiting the body's ability to synthesise protein.

The White House refused to confirm another report that plans for a covert operation against the Ansar al-Islam facility had been considered and rejected.

'Bin Laden's archive'

Extracts from 64 videos recovered in Afghanistan are being broadcast by the American network CNN, and appear to show al-Qaeda members carrying out experiments and training exercises.

Footage shows three dogs being exposed to an unidentified vapour, which causes them to vomit and writhe in agony before dying.

Other tapes show how to make bombs, kidnap people, carry out assassinations and blow up bridges.

The dog experiments appear to show a chemical capability

"This is a serious reminder of the type of enemy we're up against," said Mr Fleischer, who added that President George W Bush had been fully briefed on the tapes.

Experts have authenticated the tapes for CNN on the basis that they include footage of events and interviews held by Bin Laden, shot by al-Qaeda's own cameramen.

"This is not the library of someone else... This is [al-Qaeda's] history, the record room of Osama Bin Laden," terrorism analyst Rohan Gunaratna said.

CNN did not say where or how the tapes were uncovered, saying only that they were obtained without payment from "a source in Afghanistan, following a 17-hour drive from Kabul through treacherous terrain to a remote part of the war-torn country".

According to the TV company, almost all the tapes pre-date 11 September 2001, although one includes recorded segments from televised news reports on that day showing the aftermath of the attacks on New York and Washington.

Dead dogs

US government advisers who have seen the tapes are reported to have found them "extremely significant".

In particular they showed interest in the fact that al-Qaeda appeared to have been able to produce a "predictably lethal chemical" demonstrated in the dog tapes.

An Algerian militant, Ahmed Ressam, convicted of a millennium bomb plot in the US in 2001, gave testimony about the use of dogs in experiments with cyanide at the al-Qaeda camp where he received training in Afghanistan.

Intelligence sources quoted by CNN say the experiments probably took place at the remote Darunta camp, where satellite images have in the past included the corpses of dogs.