British police say they've arrested a 23-year-old man and his 18-year-old sister on suspicion of having terrorism-related documents.

Officers said that the pair was arrested Thursday morning in the Small Heath area of Birmingham, 120 miles (195 kilometers) northwest of London.

West Midlands Police, the local force, says the arrests were planned ahead of time and weren't made in response to any threat to public safety. They say they have seized a number of computers and other electronic devices.

The force gave few other details. British law criminalizes the collection of information "likely to be useful to a person committing or preparing an act of terrorism," for example bomb-making instructions, unless the person has a "reasonable excuse."