A second man has been arrested by detectives investigating Friday's terrorist attack at Parsons Green, which left 30 people injured when a homemade bomb exploded during peak hour, British police say.
The 21-year-old was arrested in the suburb of Hounslow in London's west just before midnight (local time), the Metropolitan Police force said in a statement.
He was detained under Britain's Terrorism Act and taken to a south London police station, the force added.
It follows the arrest of an 18-year-old man on Saturday (local time), in Dover.
The homemade bomb, which was concealed in a bucket within a shopping bag, went off about 8:20am on Friday, as the train was carrying commuters from the suburbs, including many school children.
The Islamic State group has claimed one of its units planted the bomb on the train.
More to come.