An explosion rocked the London Underground on Friday, September 15 where 29 people were injured. The Islamic State group has claimed responsibility for the dastardly attack.
"The bombing on a metro in London was carried out by a detachment of the Islamic State," ISIS said in a statement published by its Amaq propaganda agency.
UK Prime Minister Theresa May said was "clearly intended to cause significant harm".
The explosion, on a District Line Tube in the British capital's southwest, occurred as the train pulled into Parsons Green station. Commuters said they heard a bang and saw a fireball inside the carriage when the "bucket bomb" exploded.
Several people suffered facial burns; some reportedly were even trampled in the rush to escape.
Pictures of a white bucket on fire inside a supermarket bag, with wires trailing on to the carriage floor of the train went viral on social media.
Scotland Yard said that the group used improvised explosive device (IED). Some reports indicated that the suspect was identified after investigators reviewed the CCTV footage at the station.
Scotland Yard's counter-terrorism squad, SO15, has taken the lead in the investigation from the transport police.
"Deputy Assistant Commissioner Neil Basu, the senior national coordinator for counter-terrorism policing, has declared it a terrorist incident," the police said in a statement earlier in the day.
Mayor Sadiq Khan said London "utterly condemns the hideous individuals who attempt to use terror to harm us and destroy our way of life", and urged Londoners to remain calm and vigilant.
UK has raised their threat level to its highest level of 'critical'.