Police have seized computers and other material from two hospitals in Australia as part of the investigation into attempted car bombings in London and Glasgow.
Detectives also revealed that inquiries in Australia, where Indian doctor Mohammed Haneef was arrested in Queensland state on Monday, had also widened to a third state, New South Wales.
Australian Federal Police Commissioner Mick Keelty said: "There are a number of people now being interviewed as part of this investigation.
"It doesn't mean that they're all suspects, but it is quite a complex investigation and the links to the UK are becoming more concrete."
He said those being interviewed included foreign doctors of Indian background. Computers were taken from hospitals in Perth, Western Australia, and the outback mining town of Kalgoorlie.
Eight people have been arrested over the bomb plots in the UK and Australia.
Six are being held at London's Paddington Green police station.
Of those being held in London, five men are believed to be either doctors or trainee doctors. Among them is Dr Mohammed Asha, 26, of Newcastle-under-Lyme, Staffordshire. The sixth person detained is his wife, Marwa Asha, a laboratory researcher.
Meanwhile, a seventh remains in a critical condition at the Royal Alexandra Hospital in Paisley, near Glasgow, following the attack at the city's airport.
Detectives have until Saturday to question the six at Paddington Green.
