Four men were arrested under the Terrorism Act early today as part of a major ongoing investigation, police said.
Officers from the West Midlands Counter Terrorism Unit detained the men at their homes in the Sparkhill area of Birmingham on suspicion of travelling to Pakistan to undertake terrorist training and of raising funds for terrorist purposes.
A police spokesman said the suspects, aged between 19 and 24, had been arrested as part of Operation Pitsford, a large-scale inquiry which has already seen eight other people charged with a variety of offences.
A police spokesman said: "Today's arrests were pre-planned and not made in response to any immediate threat to public safety."
Officers were unarmed during the raids, the spokesman added, and detectives have an initial 48 hours to question the suspects before charging, releasing or applying for a warrant of further detention.
Eight people arrested in September have already been charged in connection with the investigation and seven of them are currently on remand after appearing in court.