6th man arrested in connection with London Underground attack Metropolitan police have arrested a 17-year-old suspect in their investigation.

 -- London Metropolitan police arrested a sixth suspect in last week's Underground train bombing in the early hours of Thursday morning.

After serving a warrant at an address in Thornton Heath, police arrested a 17-year-old male suspect under section 41 of the Terrorism Act and began a search of the property.

The arrest follows less than a day after a 48-year-old man and a 30-year-old man were arrested in Newport, South Wales, when officers executed a warrant at the address where the two men were located.

A 25-year-old man was arrested Tuesday evening, also in Newport, at a different address.

A 21-year-old man was arrested on Saturday in Hounslow, a borough in West London, by detectives with the Metropolitan Police's Counter Terrorism Command, and earlier Saturday police had evacuated a house in a London suburb as well as part of the Port of Dover after arresting an 18-year-old man that morning in the southeastern coastal city.

None of the six men who have been arrested in connection with the attack have been publicly identified. All remain in custody at a South London police station.

Thirty people were injured in the September 15 attack on a train at Parsons Green Underground station in London. Police said an apparent bucket bomb exploded during the Friday morning commute, injuring 30 people. All of the injuries were considered minor. Authorities said the bomb did not fully explode, likely limiting the number of casualties.

The terror threat was lowered to severe from critical over the weekend, but police warned the public should remain vigilant.

"This continues to be a fast-moving investigation. A significant amount of activity has taken place since the attack on Friday," said Commander Dean Haydon, head of the Met Counter Terrorism Command.

"We urge the public to report any suspicious activity to the police by calling us, in confidence, on 0800 789 321, or in an emergency by dialling 999," Haydon said in a public statement.