Another arrest made in London transit bombing, 1 person released

British police have arrested a sixth person in connection with last week's attack on a London underground train and released one man who was arrested earlier. 

Detectives arrested a 17-year-old under the Terrorism Act early Thursday in south London. A search of the property where he was found is underway.

Cmdr. Dean Haydon, head of the Metropolitan Police Service's Counter Terrorism Command, said a "significant amount of activity" has taken place since a homemade bomb partially detonated during the Friday morning rush hour, injuring 30 people. The attack sparked a manhunt for the perpetrators and prompted the government to briefly raise the national terrorism threat to the highest level.

Detectives arrested three men earlier this week in Newport, Wales. An 18-year-old refugee from Iraq and a 21-year-old from Syria who were arrested previously were also in custody, but on Thursday, police said the 21-year-old was released without charge.

• British police arrest 2 more after London subway explosion, 5 now in custody

The rest of those arrested remained in custody, but no one has been named or formally charged.