London, Dhul-Hijjah 25, 1438 H., September 16, 2017, SPA -- A manhunt was under way in London after a crude bucket bomb blew up in a rush-hour train and injured 29 people, prompting authorities to raise Britain's terrorist threat level to "critical." Officers were making "excellent progress" in the investigation, Assistant Commissioner Mark Rowley of the Metropolitan Police said without naming who they were looking for. The terrorist attack, the fifth in Britain this year, was claimed by the Islamic State jihadist group via its Amaq news agency mouthpiece. Prime Minister Theresa May said the decision had been taken to elevate the national security threat level from "severe" to "critical," the highest possible, and that the public would see more armed officers on the street and in trains. Military personnel also will replace police guards at certain public sites, May said. "This is a proportionate and sensible step which will provide extra reassurance and protection while the investigation progresses," she said in a televised address. Ambulances and fire brigades rushed to Parsons Green underground station in south-west London around 8:20 am (0720 GMT) after reports of an explosion on a train. Most of the injuries were burn-related and none of the victims are in life-threatening condition. --SPA 02:37 LOCAL TIME 23:37 GMT www.spa.gov.sa/w488383