Three of the eight people arrested in connection with the failed car bombings in Glasgow and London had links to a hospital in Paisley.
Police sealed off the doctors' accommodation in Paisley
Iraqi Bilal Abdullah, who was arrested at Glasgow Airport, worked as a locum doctor at the Royal Alexandra Hospital.
Strathclyde Police said two further men were detained at residences there, though officers would not confirm whether they were doctors.
Two controlled explosions were carried out on two vehicles at the hospital.
One of the two suspected of driving the flaming Jeep loaded with gas canisters into the arrivals hall at Glasgow Airport, suffered severe burns and remains in a critical condition.
He is under armed police guard at the same Paisley hospital.
The two men, aged 25 and 28, who were held at the hospital were detained under the Terrorism Act.
Police confirmed that an eighth man was arrested abroad on Monday.
Five people had already been arrested in connection with the Glasgow attack and the attempted London bombings.
Paisley - Burning car driven into doors of Glasgow Airport on Saturday. Two people arrested at scene
London - Two car bombs that failed to detonate found in West End on Friday
Paisley - Controlled explosion carried out on car at Royal Alexandra Hospital
Cheshire - Man and woman arrested on M6 on Saturday night, then taken to London for questioning while in Liverpool a man is arrested and police search two addresses
Houston - Police searching houses in the Renfrewshire village, near Glasgow Airport
Newcastle-under-Lyme - Police searching two addresses in Staffordshire
Strathclyde - Two men, aged 28 and 25, are arrested by Strathclyde Police
Paisley - A second controlled explosion is carried out at the doctors' quarters at the Royal Alexandra
A second doctor being held is Mohammed Asha, 26, of Newcastle-under-Lyme, Staffordshire, who was arrested in a dramatic police swoop on the M6 motorway.
Dr Asha, who trained in Jordan, is being held with his 27-year-old wife at Paddington Green police station.
Those arrested are believed to be of Middle Eastern nationalities.
Greater Glasgow and Clyde Health Board said they could not comment because of the ongoing police inquiry.
An initial controlled explosion was carried out on a car parked at the Royal Alexandra Hospital over the weekend.
On Monday, a second controlled explosion took place at the hospital's residential block just two miles from the airport building.
Police have been searching houses in the Renfrewshire village of Houston, near Glasgow Airport.
The terror alert level was raised to critical - its highest level - after a Jeep Cherokee, loaded with gas cylinders, crashed into the doors of Glasgow Airport's main terminal and burst into flames on Saturday afternoon.
Detectives are trying to trace the movements of the green Jeep Cherokee - registration L808 RDT - which crashed into the airport.
The attempted attack at the airport came a day after two Mercedes containing petrol, gas cylinders and nails were found outside a nightclub in London's Haymarket and in a nearby street. The devices failed to detonate.
Police are linking the failed bombings and the UK remains on high alert amid fears of a possible further attack.
It is understood the Metropolitan Police will be taking charge of both inquiries and are to transfer Bilal Abdullah held in Scotland to the UK capital.
Bomb disposal experts carried out a controlled explosion
It has emerged that detectives tried to contact a letting agency, believed to have rented out a house to one of the suspects, 10 minutes before the attack at Glasgow airport.
Daniel Gardiner, director of the Paisley-based Let-It agency, said officers had traced his company after tracking phone records linked to the foiled London car bomb attacks.
The UK's top counter-terrorism officer, Deputy Assistant Commissioner Peter Clarke, of the Metropolitan Police, said the links between the three attempted car bombings were becoming "ever clearer".
He described the investigation into the failed bombings as "extremely fast-moving", with forensic searches of vehicles proving "extremely valuable" and thousands of hours of CCTV being sifted through.
ABC News in America has reported that US law enforcement officials received warnings two weeks ago of terror attacks in Glasgow and Prague, the Czech Republic, against "airport infrastructure and aircraft".
Police have urged anyone with information to phone the confidential Anti-Terrorism hotline number on 0800789321.