A collection of videotapes has been uncovered in Afghanistan which appears to have belonged to top al-Qaeda leadership and may have been Osama Bin Laden's own personal archive.

Extracts from about 250 tapes were first broadcast by the American network CNN on Sunday, and are said to include experiments and training videos apparently filmed by al-Qaeda.

Whenever Osama bin Laden met with foreign journalists, he always had his own cameraman. And it is those tapes that are there

Rohan Gunaratna

Experiments with poison gas could be the first evidence that the group, which is blamed for the 11 September attacks on the US, was involved in the development of chemical weapons.

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

Other tapes reportedly show bomb-making techniques, including how to make a purified form of the explosive TNT from easy-to-obtain materials.

The tapes also reportedly show mock abductions by masked men intercepting a vehicle on a dusty road, assassinations from the back of a motorcycle, and how to blow up bridges.

'Bin Laden's library'

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 is quoted by CNN as saying.

The dog experiments appear to show a chemical capability

CNN does 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".

CNN says 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.

US government advisers shown 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.

A senior Bush administration official quoted by CNN said the footage suggested a "very strong desire" in al-Qaeda to acquire chemical weapons and "to use them against humans".

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 Bin Laden 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.