London has been hit by a powerful explosion during the rush hour this morning as commuters headed to work on the city’s subway. The blast left 22 people injured. According to media reports, an improvised explosive device (IED) went off on a Tube train in south-west London at about 8:20 a.m. local time (3:20 a.m. ET). London’s Metropolitan Police are treating the incident as an act of terror and have called in the MI5, country’s domestic counter-intelligence agency, to look into the explosion.