Heavily armed anti-terrorist police have arrested two more suspects in connection to an attack on Glasgow Airport Saturday, and attempted car bombings in London on Friday.
British police made the arrests in Cheshire, a county located in northern England.
Investigators say there are connections between the two attacks, which could have resulted in the deaths of hundreds of people.
"There are very similar features to both incidents, and through that we have linked the two," Strathclyde Police Chief Constable Willie Rae told a press conference.
On Saturday, two men tried to ram their burning Jeep Cherokee into the main terminal building of Scotland's Glasgow Airport.
Britain's security alert is now at "critical," indicating that terrorist attacks are imminent.
The two suspects were immediately arrested, but one of the men suffered severe burns in the attack and remains in critical condition.
Police also say they found a "suspect device" on the man being treated at the Royal Alexandra Hospital in nearby Paisley, and were forced to evacuate the building while they moved the device to a safe area.
It's unclear whether anyone else was in the SUV.
Police have not specified how they linked Saturday's attack to Friday's foiled car bomb plot, in which two abandoned cars packed with explosives were found in central London.
"It certainly seems that this was a coordinated attack, that it wasn't a coincidence, and is the opening of a new campaign against Britain," author and terrorism analyst Eric Margolis told Â鶹´«Ã½net.
The attacks come almost two years after the July 7, 2005 London transit attacks that killed 52 people.
"I know that the British people will stand together, united, resolute and strong," Prime Minister Gordon Brown said in a televised statement.
Witnesses at the airport said the men drove at full speed through security barriers and into the glass doors at the entrance of the terminal.
Both men, one of them on fire, then exited the vehicle, say witnesses.
"The car came speeding past at about 30 mph. It was approaching the building quickly," Scott Leeson, who was nearby at the time, told The Associated Press. "Then the driver swerved the car around so he could ram straight in to the door. He must have been trying to smash straight through."
Leeson said only the nose of the green SUV made it inside the building.
"He's trying to get through the main door frame but the bollards (security posts) have stopped him from going through. If he'd got through, he'd have killed hundreds, obviously," he said.
At the scene, passengers fled running and screaming as flames and black smoke rose from the vehicle.
Witness Stephen Clarkson, who said he helped police restrain one of the men, told the BBC that the man on fire was a large South Asian man.
"His whole body was on fire.... He was just talking gibberish," Clarkson told the BBC.
Another witness Richard Grey said police "wrestled him (the man on fire) to the ground -- the fire was burning through his clothes -- and finally put him out with a fire extinguisher."
A maintenance worker at the airport said it seems like the men deliberately tried to set the car on fire.
"It looked like they had molotov cocktails with them," Thomas Conroy told the BBC.
"They sort of burst them round about the flames to make sure the car would go up big style."
White House spokesperson Tony Snow said some U.S. airports would tighten security, but the country's overall terror alert status would not change.
"The most you're going to see right now is some inconvenience -- some increased inconvenience of airline passengers, more likely at large airports than small," said Snow.
In Canada, Greater Toronto Airports Authority spokesperson Scott Armstrong said officials are already on alert, but that the attack on Glasgow is "very localized."
Vancouver International Airport spokesperson Ali Hounsel said security remains the same, and any change would have to be ordered by the federal government.
There were no flights to Glasgow scheduled from the Vancouver airport on Saturday.
With files from The Associated Press and The Canadian Press
