British police arrested a 19-year-old man Friday on suspicion of a terrorism offense over a suspicious package discovered on a London subway train.

The Metropolitan Police force said officers used a stun gun while detaining the man at midday Friday on a busy city street. Specialist firearms officers were deployed for the arrest, but did not fire their weapons.

The man is being held at a London police station on suspicion of “the commission, preparation and instigation of terrorism acts.”

North Greenwich subway station on the Underground’s Jubilee Line was closed for several hours Thursday after the discovery of what police called a “suspicious item” on a train.

The object was destroyed in a controlled explosion. Police say they await the results of a forensic examination to discover what it contained.

Police say they are not looking for anyone else as part of the investigation and are keeping an open mind about motive.

Britain’s official threat level from international terrorism stands at “severe,” the second-highest point on a five-point scale, meaning an attack is highly likely.

“Thanks to the outstanding professionalism of the Metropolitan Police, Transport for London staff and the British Transport Police, this situation was dealt with swiftly and safely, and no injuries resulted,” London Mayor Sadiq Khan said.

But Manuel Cortes, secretary general of the TSSA union representing some Underground staff, said government budget cuts would make it impossible for transit staff and police “to exercise the levels of vigilance now necessary to keep London open for business and our people and our passengers safe.”

(AP)