Anti-terror police have arrested seven people after a long-running intelligence operation into a suspected "international" threat from Islamic extremists.

Unarmed officers raided 14 addresses across Birmingham on Sunday night after taking the decision to step in "to ensure public safety". Forensic teams took away computer equipment and a car for further investigation while searches continued at the properties.

West Midlands Police said the detentions were not linked to the Liberal Democrat conference which is taking place in the city and declined to comment on the possible target of any feared attack. Because the officers were unarmed, it is not believed the suspects posed an imminent danger.

Six men aged between 25 and 32 were arrested at their homes on suspicion of the commission, preparation and instigation of terrorism in the UK. Among them was a taxi driver, a gym instructor and an Islamic preacher, according to neighbours.

A 22-year-old woman was arrested early yesterday morning on suspicion of failing to disclose information contrary to the Terrorism Act 2000.

Two of the arrests on Sunday night took place in the Sparkbrook area of Birmingham, one of two largely Asian suburbs of the city where 217 CCTV and automatic-number-plate-recognition cameras were deployed in a £3m anti-terrorist initiative.

They were taken down in June following anger from the local community and threats of legal action.

West Midlands Police's Assistant Chief Constable for Security, Marcus Beale, said the intelligence-led inquiry had been going on for some time and had been subject to a series of reviews.

"As a result of one of those reviews... we decided that the time was right and moved to make six arrests during the night, with a further one a few hours later," he said.