Australian police have detained an Indian doctor over the failed car bombings in the United Kingdom, and have been speaking to another doctor.
Gold Coast Hospital said the doctor had excellent references
They are questioning the first man, named as Mohammed Haneef, 27, at the request of UK police, but say he has not been charged.
The second man is being interviewed as a result of the first arrest.
Seven other people are being questioned in the UK about the attempted attacks in central London and Glasgow airport.
It is understood Mr Haneef had been in phone contact with those suspected of involvement in the London and Glasgow incidents, says the BBC's Gordon Correra.
Detectives want to know if he had any prior knowledge of the attempted attacks, he adds.
Mr Haneef was picked up at Brisbane airport after a tip-off from British police, officials said.
He trained as a doctor in his native India and arrived in Australia in September 2006 following a period spent in Liverpool.
But Australian police have been downplaying the significance of the second man in the investigation.
Plea for calm
Australia's Attorney General Philip Ruddock said federal and state police had been acting on British intelligence when they detained Mr Haneef at Brisbane airport.
He was reported to have been carrying a one-way ticket to India.
30 June Two men arrested at Glasgow airport after burning car driven into doors of main terminal
30 June A 26-year-old-man, Dr Mohammed Asha, and a 27-year-old woman arrested on the M6 near Sandbach, Cheshire
1 July A 26-year-old man arrested near Liverpool's Lime Street station
1 July A 28-year-old man and a 25-year-old man arrested in Paisley
2 July A 27-year-old male doctor is detained in Australia, and a second doctor is questioned
"The man is currently assisting police with their inquiries. No charges have been laid," Mr Ruddock told reporters.
The doctor had been working as a registrar at the Gold Coast hospital in Queensland, having been sponsored by the Queensland health department, officials said.
He moved there after answering an advert in a British medical journal while working at a hospital near Liverpool.
Queensland Premier Peter Beattie said the doctor had been regarded by the hospital as a "model citizen" who held excellent references.
Police raided his home following the detention, and were seen by neighbours carrying away bags of items and computer disks.
Officials confirmed to reporters that a second man - who had also worked as a doctor around Liverpool - was also being interviewed, but said there was no link between him and the attacks.
'No Australia threat'
Under Australia's counter-terrorism laws, suspects can be held for three days without charge and for longer periods with the approval of a court.
Prime Minister John Howard urged Australians to stay calm after the arrests, saying that there "has been no change to our security position".
"We have no information that there is now a greater likelihood of any terrorist incident in Australia than there was late last week," he said.
A major investigation has been under way in the UK since two cars containing petrol, gas cylinders and nails were discovered in central London in the early hours of Friday. They failed to explode.
One day later, a burning car loaded with gas cylinders was driven at the main terminal building at Glasgow's international airport. Two men were arrested at the scene and are now in custody.