A four-wheel-drive vehicle rammed into Glasgow airport's main terminal on Saturday and exploded in flames in what police described as an attack, a day after a twin car-bomb plot was foiled in London.

Britain's Home Office announced shortly after the incident that it had raised the national security alert level to "critical", the highest possible ranking, and one which indicates further attacks are expected imminently.

Scottish police said Saturday there was a likely connection between the Glasgow attack and the foiled car bombs in London. Prime Minister Gordon Brown convened a meeting of Britain's top security committee on Saturday to discuss the events in Glasgow.

	Advertisement

"I can confirm that we believe the incident at Glasgow airport is linked to the events in London yesterday," the chief constable in the Glasgow area, Willie Rae, told reporters.

"There are clearly similarities and we can confirm that this is being treated as a terrorist incident."

In Kennebunkport, Maine, the United States announced it was boosting security at airports nationwide, although the overall U.S. terrorism threat level would remain the same.

In Glasgow, police said two people were arrested following the blaze at the terminal entrance. Witnesses described those arrested as Asian men and said one of them was badly burnt.

Witnesses told the BBC the vehicle, a green Jeep Cherokee, exploded shortly after crashing into the glass front doors of the terminal, and said there was a heavy stench of gasoline.

"It raced across the central reservation and went straight into the building," said taxi driver Ian Crosby outside the terminal.

Crosby said a stocky Asian man had got out of the car and was quickly wrestled to the ground by bystanders.

"I think this was a terrorist attack," Crosby said.

Another witness said the occupants of the car had got out of the vehicle after they crashed it into the building and taken out cans of petrol that they then used to douse the car, before it went up in flames.

The airport was shut down following the incident.

In London, police scoured hours of footage from security and traffic cameras, and extra squads were deployed on the streets, particularly around landmarks such as the Houses of Parliament after Friday's failed car bomb attacks in the center of the city.

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

A mobile phone, which security experts believed might have been a detonation device, was left inside the fume-filled car.

A second Mercedes packed with gas and nails was later found to have been parked just a few hundred yards from the first.

British authorities said the two vehicles were "clearly linked." Both bombs were quickly defused but, had they gone off, would have caused significant injuries and deaths, police said.

The foiled plot came to light two years after a coordinated attack by suicide bombers on London's transport system killed 52 commuters. It appeared to have similarities to an earlier plot in which an al-Qaida militant planned to blow up gas-filled bombs inside limousines in London.

Plans for policing of public events in the coming 10 days were reviewed to ensure public security, including the Wimbledon tennis tournament and a concert for Princess Diana on Sunday.

Intelligence sources believe there is a growing probability the London plot was hatched by an al-Qaida-style group.

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

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