Five men have been arrested on suspicion of preparation or instigation to commit acts of terrorism, on 27 August, with police being granted a further seven days to complete questioning.
Bomb disposal officers were sent to Lee Bank, in Birmingham, and three men aged 18,24 and 28 were arrested, with a further two men aged 32 and 37 arrested in Stoke-on-Trent.
According to a spokesman from the West Midlands Counter Terrorism Unit, detectives appeared before London's Westminster Magistrates' Court via video link on Saturday to submit their request for a warrant of further detention.
Ch Supt Sue Southern, from West Midlands Police, said: "The arrests of the five men were intelligence led and our investigation continues at full pace."
It is understood that a number of properties in the Stoke and Birmingham areas have been searched as part of the investigation.