Britain deployed hundreds of soldiers at strategic sites on Saturday to free up police to hunt those behind a bomb which injured 29 people on a packed commuter train in London and triggered the country’s highest security level.

Prime Minister Theresa May said the critical threat level meant an attack may be imminent, after a bomb engulfed a carriage in flames and sparked a stampede during the Friday morning rush hour in west London .

The home-made bomb , which apparently failed to detonate properly, was the fifth major terrorism attack in Britain this year and was claimed by Islamic State. The militants have claimed other attacks in Britain this year, including two in London and one at a pop concert in Manchester.

The attack at Parsons Green tube station prompted the government to take the rare step of deploying soldiers.