Police faced a deadline Tuesday to release nine suspects in an alleged terrorist kidnap plot or to seek court permission for further interrogation.
News reports, citing unidentified sources, said the alleged plot was to kidnap, torture and behead a Muslim British soldier.
West Midlands Police say they have completed searches of 18 properties raided last week, the AP reports.
The suspects, detained on suspicion of the commission, instigation or preparation of acts of terrorism, are being held in Coventry in central England.
Eight of the suspects were arrested in early-morning raids on Wednesday, and the ninth was arrested later in the day.