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london train attack

U.K. police make 'significant' arrest in London train blast investigation

U.K. police on Saturday arrested an 18-year-old in possible connection with an explosion in a London Underground train that injured at least 29 people Friday. "We have made a significant arrest in our investigation this morning," Deputy Assistant Police Commissioner Neil Basu said, according to The Associated Press.

The man was arrested in the port of Dover on the English Channel, where he may have been trying to board a ferry to leave the U.K., The Guardian reported. He is being questioned under the Terrorism Act, but has not been charged, and his name is not being released.

The Islamic State claimed responsibility for the attack, which occurred during the morning rush hour at the Parsons Green station. Counterterrorism officials say the improvised explosive device only partly detonated, and had a timer attached to it. Police are poring over CCTV footage and hinted that more suspects may be at large.

British Prime Minister Theresa May has raised the terrorism threat level in the U.K. to "critical," the highest possible level, indicating a threat is "expected imminently."