Police said they arrested four men in Birmingham on Tuesday as part of an ongoing counter-terrorism investigation that has uncovered an alleged suicide bombing plot.
The men, three aged 19 and one 24, were detained under counter-terror laws in the Sparkhill area on suspicion of fundraising for terrorist purposes and of travelling to Pakistan to undertake terrorist training.
"Today's arrests were pre-planned and not made in response to any immediate threat to public safety. Officers were unarmed," said a statement from West Midlands Police.
They are the latest arrests in a counter-terror investigation in the city which was launched in September.
Police say eight people have so far been charged as part of the probe, with seven remanded in custody after appearing in court in London.
Three men were charged with "planning a bombing campaign" and "stating an intention to be a suicide bomber".
Other charges the suspects faced included collecting money for terrorism, travelling to Pakistan for training in bomb making and making a "martyrdom" film.