The search is still underway for the person who planted an improvised explosive device on a District Line tube yesterday morning.
The Metropolitan Police issued a statement late last night urging members of the public with information about the terror attack to contact them.
The Met's head of national counter terrorism policing, Mark Rowley, added that the independent Joint Terrorism Analysis Centre has raised the UK's threat level from international terrorism to critical. This means that a further terrorist attack is not only highly likely, but may be imminent.
“Hundreds of police officers are pursuing numerous lines of enquiry, trawling through hours of CCTV footage and speaking to witnesses," said Rowley.
“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.”
No one died in yesterday's attack at Parsons Green tube station, but 29 people were injured.
Anyone with information is urged to call the Anti-Terrorist Hotline on 0800 789 321, and people with footage or images from the incident are urged to upload them at www.ukpoliceimageappeal.co.uk where they will be looked at by investigators.
As of last night, detectives had spoken to 45 witnesses and were continuing to receive information from the public to the confidential anti-terrorist hotline.
The Met said the public had sent 77 images and videos to investigators via the UK Police Image Appeal website.
Following the incident, military personnel have been drafted in to protect national infrastructure sites allowing additional armed police officers to carry out patrols.
The police said security checks at large events will be enhanced, which may cause disruption, and people should avoid taking bags to events where possible.
Read more: Parsons Green explosion: What we know so far