Kent Police on Saturday arrested an 18-year-old man in connection with the London Parsons Green explosion, which has left 30 people injured, British police said.
The man was arrested in the port area of Dover on Saturday morning under section 41 of the Terrorism Act, police said in a statement, adding that the arrest was "significant".
British police said they evacuated and searched a residential address in Sunbury of Surrey after making the arrest.
Nationwide manhunt is underway in the country to nab the suspects. Friday's rush-hour tube explosion in London was declared a terrorist attack.
ISIL has taken credit for the attack as reported by its Amaq news agency.
The country's terror threat level has been raised to "critical" – indicating a further attack may be imminent, Prime Minister Theresa May announced late Friday following the attack.