LONDON  (AFP) – British police said on Monday they had arrested six men and a woman in Birmingham as part of a major pre-planned counter-terrorism operation targeting Islamic extremists.

The men, aged between 25 and 32, were detained by unarmed officers on suspicion of the commission, preparation or instigation of an act of terrorism in Britain, West Midlands Police said in a statement.

Police sources said the operation targeted Islamists.

Unarmed officers arrested the suspects at or close to their homes in Britain’s second biggest city between 11:30 pm (2230 GMT) on Sunday and 01:00 am on Monday, it said.

In addition, a 22-year-old woman was arrested on Monday on suspicion of failing to disclose information which could have used in assisting the prevention of an act of terrorism, said police.

Police said the suspects, who were all British passport holders, were being held for questioning in the Birmingham area.

“The operation is in its early stages so we are unable to go into detail at this time about the nature of the suspected offences,” assistant chief constable Marcus Beale said.

“However, I believe it was necessary to take action at this time in order to ensure public safety.”

Police said the arrests were not connected to the annual conference of the Liberal Democrat party, the junior partner in the coalition government, which is currently taking place in Birmingham.