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.
Earlier on Saturday (local time) police arrested an 18-year-old man in the city of Dover — the main ferry link to France — and raided a property in Sunbury, a small town outside London, as they hunted for whoever planted the device.
Hounslow is about six kilometres from Sunbury, where police raided and searched a building in connection with the bombing.
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.
Britain's terror threat level remains at critical — the highest level — meaning authorities believe another attack is imminent.
More to come.