Seven men have been arrested on suspicion of terror offences after firearms and other weapons were found "hidden" in a car.
West Midlands Police said one man from West Yorkshire and six from the West Midlands are being questioned on suspicion of the commission, preparation or instigation of acts of terrorism following a series of arrests this week.
A spokesman said: "The arrests followed a routine stop of a vehicle by police on the M1 motorway in South Yorkshire on Saturday June 30.
The car was impounded on suspicion of having no insurance.
Firearms, offensive weapons and other material were later found hidden inside, prompting police to take action to trace and arrest the driver, passenger and others suspected of being involved."
Police said three men aged 23, 26 and 27 from Sparkhill, Birmingham, were arrested on Tuesday morning.
Three more suspects, a 22-year-old from Alum Rock, Birmingham, a 24-year-old from the Moseley area of the city and a 22-year-old from Smethwick, West Midlands, were arrested on Wednesday evening.
A 43-year old man from Kirklees, West Yorkshire, was detained yesterday.
Police said the contents of the car were undergoing forensic analysis and the suspects' homes had been searched.
Detectives have until next Tuesday morning to question the three men arrested on Tuesday, after the initial 48-hour detention period ran out.