Ivonne Geller, 49, a tourist from Mexico strolling outside Tiger Tiger, the nightclub outside which one of the car bombs was left, said: "You could be safe anywhere or you could be safe nowhere.

It hasn't put me off travelling here. I just feel angry about the methods of these people who try to harm innocent people."

Fume-filled car

A major counter-terrorism investigation was launched after the discovery in the early hours of Friday of a metallic green Mercedes packed with up to 60 litres of fuel, several gas canisters and a large quantity of nails.

The vehicle was parked outside the nightclub, in the theatre district of London, and aroused suspicion only after ambulance workers, treating someone else, thought they noticed smoke inside the vehicle.
   
On inspection, a mobile phone, which security experts believe may have been a triggering device, was found inside the abandoned, fume-filled car.
 

The Mercedes was parked in
London's busy theatre district [AFP]

A second Mercedes packed with gas and nails was later found to have been parked just a few hundred yards from the first, before it was towed away by traffic wardens in the early hours of Friday for violating parking restrictions.

Police said the two vehicles were clearly linked and that although both bombs were quickly defused, had they gone off they would have caused significant casualties.

Al-Qaeda suspected
 
Intelligence sources believe there is a rising probability that the plot was hatched by an al-Qaeda-style group.

A source said: "The feeling it is Islamist, rather than the other possibilities, is very quietly growing stronger."

The area of London where the car bombs were left, known as the Haymarket, is one of the busiest in the capital and one of the most intensely monitored by CCTV surveillance.

Police said they were studying hundreds of hours of footage in the hunt for possible suspects.

ABC, the US television channel, reported that a "crystal clear" image of a suspect had been found, but British police would not confirm that.

Security sources said an important angle of investigation was a website called al-Hesbah, which carried a posting by a regular contributor on Thursday saying that London was going to be bombed, according to CBS television.

"It will obviously be a line of enquiry," the source said.

The Scotsman newspaper reported that an Iraqi man who absconded from police monitoring 11 days ago was also being sought.