An incident in which a car was driven at Glasgow Airport's main terminal and burst into flames is being treated as a terror attack by police.
The suspect is in a critical condition at the Royal Alexandra Hospital
Strathclyde Police also said the attack was being linked with the car bombs found in central London on Friday.
The force's Chief Constable Willie Rae said: "There are clearly similarities and we can confirm this is being treated as a terrorist incident."
Two men were arrested following the attack at 1515 BST on Saturday.
Two further arrests were made in Cheshire in connection with the incident in Glasgow and the car bombs found in London's West End.
Anti-terror police from the Metropolitan Police's Counter Terrorism Command assisted by officers from the West Midlands Counter Terrorism Unit made the arrests, Scotland Yard said.
Mr Rae earlier told a news conference in Glasgow that the suspect at the city's Royal Alexandra Hospital was being treated for severe burns and was in a critical condition.
He said a 'suspect device' had been found on the suspect.
"As a consequence of that, the hospital was partly evacuated until the device was removed and put into a safe area," he said.
Experts later found the item was not linked to any explosive and it was declared safe, however the hospital's A&E remains closed.
Mr Rae said the second man was being detained in police custody.
The vehicle at the airport is now considered safe, and will be subject to full forensic investigation as part of the ongoing police investigation. It is expected to be removed later in the morning.
A detailed search is still continuing within the airport and the area will remain cordoned off until this is complete.
He said the airport had been evacuated and a number of passengers had been "stranded on the tarmac" as a result.
"It would have been unwise to evacuate them into the terminal building," he said.
The chief constable added: "We believe the incident is linked to events in London yesterday.
"There are clearly similarities and we can confirm this is being treated as a terrorist incident."
"There was no prior intelligence to suggest that Scotland was going to be the target of a terror attack," he added.
He said the force was working alongside the Metropolitan Police's counter terrorism officers.
Deputy Assistant Commissioner Peter Clarke, who has responsibility for terrorism throughout the UK, was travelling to Glasgow.
Police forces across the country are on high alert after the national terrorism threat level was increased to critical.
One member of the public received a leg injury as a result of the attack but there were no other casualties.
About 2,300 passengers are being coached from Glasgow Airport to a reception centre at the SECC, where they will be reunited with friends and family.
All flights to and from the airport were suspended after the attack on Saturday.
The airport reopened to incoming flights at 0737 BST when a plane from Ibiza landed, and first departure is expected at 0900 BST.
Anyone due to fly during Sunday should confirm the status of their flight with their airline before leaving for the airport.
Chief Constable Rae appealed to about 20 to 30 people who were outside the terminal building at the time of the attack to come forward.
He also asked the public to be extremely vigilant and urged anyone with information about the attacks to phone the police incident room on 0800 056 0944.