A teenager has been charged with attempted murder and causing an explosion in relation to the bombing of a London Underground train a week ago.

Ahmed Hassan, 18, of Sunbury in Surrey, a county south of the capital, will appear at the Westminster Magistrates' Court in central London on Friday afternoon, the London Metropolitan Police said. He was arrested in the port town of Dover on Saturday.

The charge came after London's police chief said the bomb that failed to fully detonate was loaded with explosives and shrapnel.

Metropolitan Police Commissioner Cressida Dick told LBC radio: "That was a very, very dangerous bomb.

"It partially detonated, it had a large quantity of explosive and it was packed with shrapnel. It could have been so much worse than it was."

The bomb exploded at 8:20 a.m. local time last Friday on a District Line train in Parsons Green, west London.

Thirty people were injured in the blast and subsequent stampede, but none of the injuries were thought to be life-threatening.

Six men were arrested in connection with the bombing. Two of them were released without charge Thursday, and three remain in custody but have not been charged. The Islamic State claimed responsibility for the attack.

One of those released was a 21-year-old from Syria. The man’s employer said his mother suffered a heart attack after hearing of her son’s arrest.