One of the men in the car was in critical condition at a hospital with severe burns, while the other was in police custody, said Scottish Police Chief Constable Willie Rae. Five bystanders in Glasgow were wounded, although none seriously, police said.

Rae said a suspect device had been found on a man wrestled to the ground by officers and hospitalized in critical condition with severe burns.

Police later arrested two more suspects in the London and Glasgow plots in Cheshire county in northern England, Scotland Yard said early Sunday.

“I can confirm that we believe the incident at Glasgow airport is linked to the events in London yesterday,” Rae said at a news conference. “There are clearly similarities and we can confirm that this is being treated as a terrorist incident.”

Meanwhile, authorities searched several homes near Glasgow “as part of the ongoing inquiry into the incidents in Glasgow airport and London,” police said in a brief statement.

Britain raised its terror alert to “critical” — the highest possible level — and the Bush administration also announced plans to increase security at airports and on mass transit in the United States.