LONDON — The British police said on Saturday that they had arrested an 18-year-old man in connection with the terrorist explosion in a London subway station that injured at least 30 people and unleashed panic among fleeing passengers.

The suspect was detained in the port area of Dover, in the southeastern county of Kent. The police said he would be transferred to a South London police station later.

“We have made a significant arrest in our investigation this morning,” Deputy Assistant Commissioner Neil Basu, the top counterterrorism official at the Metropolitan Police in London, said in a statement. The suspect was not identified further.

The Islamic State claimed responsibility for the blast on Friday in a statement that said “a detachment” of its militants had carried out the attack.