A teenager and two men have been arrested in armed raids on addresses in east London by counter terrorism police along with a fourth arrest in the Midlands as part of a widespread investigation into “Islamist extremist activity”.

The east London operation was supported by armed officers, Scotland Yard confirmed last night.

No shots were fired, although one of the men being arrested was bitten by a police dog. He was taken to hospital where he remains for treatment. The others were being held in police cells.

The Counter Terrorism commands of both Met and East Midlands forces carried out simultaneous raids as part of the operation looking into links with “suspected Islamist-extremist-motivated offences in the UK”.

A 27-year-old, a 31-year-old and a 17-year-old youth were arrested at two east London addresses. Police aren’t revealing exact locations. A 32-year-old was arrested in Leicestershire.

Detectives have been granted warrants to detain the four who were held on Thursday, July 9, to keep them in custody for up to a week. Detention warrants on the three men expire next Thursday, July 16, while the youth can be held up to July 14.

All four are being detained on suspicion of being concerned in commissioning, preparing or instigating acts of terrorism, under the 2000 Terrorism Act.

Detectives are understood to be currently searching four addresses in east London and south London and a fifth in Leicestershire, with the investigation continuing.