A number of passengers on a London Underground train were injured and some reported being "badly burned" after an explosion caused a "fireball" in a terror attack during the morning rush hour in the city. The Metropolitan Police have called it an "act of terror", which makes it the fourth attack this year in London. London Ambulance Service tweeted that 18 people have been taken to a number of hospitals in the city. "We have taken 18 patients to a number of London hospitals. None are thought to be in a serious or life-threatening condition #ParsonsGreen," the tweet said.