Four of the ten men arrested at the weekend in connection with suspected international terrorism in the UK have been released without charge.
Three residential addresses are being searched
The men had been held on suspicion of the commission, preparation or instigation of acts of terrorism.
Of the ten, three were detained in Croydon, London, four in Wolverhampton and three in Derby, early on Saturday.
Those released had been arrested in Wolverhampton. It follows the release of one of the men arrested in Derby.
The five remaining men are being held in custody and detectives have been given until Saturday to continue questioning them.
The men are being held in London on suspicion of the commission, preparation or instigation of acts of terrorism under the Terrorism Act 2000.
The weekend arrests were not connected to the investigation into the July London bombings, said Scotland Yard.
Officers raided three residential addresses following an "intelligence-led investigation involving police and the security service", said the Met on Saturday.
The anti-terrorist branch was helped by local officers from the Met, West Midlands and Derbyshire police forces.
Forensic searches of the addresses were expected to continue for some time.
A resident in Lewis Avenue, in the Moseley Village area of Wolverhampton, said up to 20 people had stayed at the address raided there at any one time.
One man said: "There was always activity in the early hours of the morning. Men would be carrying plastic bags and packages to and from the house."
A woman added: "They were quiet, kept themselves to themselves, but I always thought there was something strange going on."