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LONDON — Counterterrorism police arrested a teenager in London on Friday after a "suspicious item" was found on the subway, officials said.

The 19-year-old suspect, who has not been identified, was shot with a Taser and detained in north London, according to a statement from the city's Metropolitan Police.

The force said he was arrested on suspicion of "the commission, preparation and instigation of terrorism acts."

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The arrest came around 24 hours after officers were called to North Greenwich subway station, in the southeast of the city, to reports that a suspicious item had been left on a train.

The station was evacuated and police carried out a controlled explosion.

"The item is currently being forensically examined and we await the results of that examination," the Met said Friday. It said officers "have been working tirelessly since the item was found to follow up all potential leads."

Related: Cops Without Guns Dominate as London Awaits 'Likely' Attack

A source at Transport for London, which runs the capitals subways and buses, told the London Evening Standard that the item was a bag "full of wires," although NBC News was not able to independently confirm this.

Police say they are keeping "an open mind" with regard to the motive and are not looking for anyone else in connection with the incident.

After a year of attacks in Paris, Brussels, and elsewhere, British officials say an attack "an attack is highly likely" and that "it is a case of when, not if" London is hit.