Missilegate: Is this conspiracy or hoax?

And now: Missilegate. A top-secret, and officially banned, United States navy "chainsaw" missile accidentally destroyed a TWA jumbo jet and 230 people off Long Island last July, a report claimed yesterday.

The US government has covered up its involvement, from a mixture of embarrassment and determination to preserve the secrecy of the weapon, according to Pierre Salinger, journalist, former spokesman for President John F Kennedy and leader of a freelance investigating team.

Mr Salinger told a press conference in Paris yesterday that his group of ten experts, including several government officials, had reached these conclusions on the mysterious fate of flight TWA800 with "very great certainty".

But the FBI, which was given the Salinger report four days ago, dismissed its findings as a "cruel hoax". There was no clear evidence that a missile destroyed the plane, the FBI said, although this remained one of three possibilities. The other two were a terrorist bombing or a mechanical malfunction.

Mr Salinger has been preoccupied by the unexplained destruction of the New York to Paris flight since he saw allegations of an accidental missile strike on the Internet. He called yesterday on the US Defense Secretary, William Cohen, to order an official investigation into the affair, which he dubbed "Missilegate".

The report, co-ordinated by Mr Salinger through the Internet, says TWA800 was "destroyed by accident ... by a US navy missile which mistook its target".

This missile - probably a top-secret kinetic-energy or chain-saw missile containing no explosive warhead - was fired either from a submarine or from a missile ship engaged in secret military exercises, the report said.

Mr Salinger produced stills of a video recording of radar screens taken at JFK Airport that night which, he claimed, showed a "missile heading towards the TWA plane". The Pentagon insists that no missile has been fired in the area for two years but Mr Salinger said 154 witnesses on Long Island saw one or two missiles in the air that night. He said he had also been contacted by a man with a son in the US Navy. The man said his son had told him: "Dad, we destroyed the plane."

The video stills of the alleged radar traces of the missile appeared in Paris-Match magazine yesterday and Mr Salinger said the proceeds from the publication of the photograph would go to the families of the TWA800 victims.

Families of French victims of the disaster decided at the weekend to begin a civil action against an unknown culprit in the French courts. This is likely to bring about a judicial investigation.

A chain-saw or kinetic-energy or continuous rod missile is a fearsome weapon, officially banned by international treaty. It contains no warhead as such and, in flight, resembles a huge rod of metal. When it finds its target it blasts straight through and would tear an aircraft to pieces.