London attack: Police counter-terror chief deploys extra 1,000 armed officers to help hunt suspects

Assistant Commander Mark Rowley says they are continuing to 'chase down suspects'

Extra armed police will be on the streets in the coming days as police hunt the bomber (Getty)

Scotland Yard's top counter-terrorism officer has announced there will be an extra 1,000 armed police on the streets in the wake of a terror attack on a Tube station in west London.

Assistant Commander Mark Rowley said there would be an increased police presence on the streets of the capital as the terror threat level is raised from "severe" to "critical", meaning an attack is imminent.

In a televised statement he said people would see extra police on the streets in the coming days, while members of the military are sent to strategic sites such as nuclear power stations, as Operation Temperer goes into effect.

He said: "Our investigation is continuing at speed and our priority is to identify, locate and arrest those responsible.

"Hundreds of police officers are pursuing numerous lines of enquiry, trawling through hours of CCTV footage and speaking to witnesses.

"The device and remnants left at the scene have been taken away and are being examined by forensic experts. While this work is ongoing, there is no doubt in my mind that those responsible intended to cause great harm and injury.”

"So far, detectives have spoken to 45 witnesses and continue to receive information from the public to the confidential anti-terrorist hotline."

He said they were currently "chasing down suspects" behind the bombing and declined to give out any more information which may threaten their investigation.

Witnesses reported seing an explosion and a "fireball" on a District Line Tube train near Parsons Green station at 8.20am on Friday.

At least 29 people have been treated in hospital for flash burns and others were injured in the stampede to escape the above ground station. NHS England said none of the victims are in a serious condition.

Footage from the incident showed a burning plastic container in a shopping bag with black, white and red wires coming out of it.

The bomb was reportedly on a timer which could be detonated remotely, security sources have said.

This is the first time the threat level has been raised to critical since the Manchester Arena bombing in May. Typically it remains for a few days before returning to severe, allowing police extra resources to hunt for the perpetrator and any accomplice.

Isis have claimed responsibility for the attack via their propaganda arm, Amaq, but Assistant Commander Rowley said it was routine for the group to claim responsibility regardless of whether they were actually involved.