Britain's anti-terror chief says the probe of failed terrorist attacks in London and Glasgow is "extremely fast moving," and says links between the events are becoming "clearer and clearer."
Peter Clarke said Sunday investigators are also learning more about the planning of the attacks but has yet to give any details.
Five suspects have been arrested, including the driver who set himself on fire before ramming his Jeep into a Glasgow airport terminal Saturday, causing the vehicle to explode. He is hospitalized with critical burns. Another person in the car was also arrested.
Police in northern England also have arrested three suspects in connection with the two failed car bombings Friday in London. Authorities spotted the cars before they could be set off. One of the cars, packed with gasoline and nails, was parked outside a central London nightclub.
Britain has raised the security alert to its highest level -- critical.
Glasgow police Sunday carried out a controlled explosion of a suspicious car parked at the hospital where one of the airport attackers is being treated. Authorities released no information on the car or its owner.
Prime Minister Gordon Brown told British television Sunday that the country faces a "long-term" threat from extremists linked to al-Qaida. But he said Britain will not yield or be intimidated.