The Sunday Times yesterday published a leaked advisory to "oil, gas, and transportation sectors" from the US department of homeland security that warned of intelligence about a plot to target petrol stations in the next month or so.
The intelligence suggested that the plan was for multiple small terror cells to launch choreographed attacks in Britain, New York, Chicago and Los Angeles.
The leaked report states: "Al-Qaida leaders plan to employ various types of fuel trucks as vehicle-borne improvised explosive devices in an effort to cause mass casualties ... The stated goal is the collapse of the US economy."
However, a spokeswoman for the department for homeland security said the warning was uncorroborated and from a single, unreliable source. The spokeswoman, Katie Montgomery, added that the warning did not refer specifically to London.
She said: "The source of the information has questionable reliability ... at this time the department for homeland security does not have any specific credible information that suggests a terrorist attack in the US is imminent."
The leaked report cites al-Qaida's Khalid Sheikh Mohammed, who is believed to be one of the masterminds behind the September 11 2001 attacks in the US, and who was arrested in Pakistan in March 2003. The leaked bulletin says that Sheikh Mohammed had told interrogators that he drew up plans to target petrol stations.
The report says he thought of using petrol trucks because of their "apparent vulnerability and the potential destructive force of a fuel-driven explosion".
Terrorists have used petrol tankers as mobile bombs before in the Middle East. A fuel tanker attack on the Khobar Towers in Saudi Arabia in 1996 killed 19 US servicemen. A month ago almost 100 people were killed in a town south of Baghdad when terrorists exploded a tanker.
The bulletin says the new alleged plot is to mount an attack before September 19, to roughly coincide with the fourth anniversary of the September 11 attacks.
British security officials have been anxious for some time that terrorists could use a vehicle to attack targets in London. Lord Stephens, the former commissioner of the Metropolitan police, warned before stepping down of an attack on a "soft target" such as a nightclub in the capital, similar to the bombings in Bali in 2002, which killed 202 people.
Concrete security barriers, aimed at stopping vehicle suicide bombers, have been established in some areas of the capital at key sites, including outside parliament.
A spokesman for the Department for Transport told Guardian Unlimited that no specific warnings had been given to the transport sector relating to the US security bulletin to American oil and transportation sectors.
The spokesman said the security of roads and other transport areas was "constantly reviewed" and that tighter security had been developed since September 11 2001.
New laws about the security of transporting dangerous goods in the UK came into force on July 22 2005. They require companies or organisations to obey certain security requirements.
These include only offering dangerous goods to carriers that have been appropriately identified; making sites that temporarily store dangerous goods secure; having a security awareness training programme in place and having a security plan in place if involved with "high consequence" dangerous goods.
