Police in the United Kingdom have arrested an 18-year-old man in connection with a bomb attack in the London Underground.
Officials said the suspect, who was not identified, was detained in the port city of Dover on September 16 and described the development as "significant."
No further details were released, and officials did not say whether they were searching for additional suspects.
A bucket packed with nails and explosives blew up on a crowded Underground train at London's Parsons Green station on September 15, injuring 30 people.
The station reopened for service early on September 16, but British Prime Minister Theresa May ordered the country's terrorism alert raised to its highest level, "critical."
"Although we are pleased with the progress made, this investigation continues and the threat level remains at critical," read a statement from Neil Basu, senior national coordinator for counterterrorism policing.
The Islamic State (IS) extremist group through its Amaq propaganda agency claimed responsibility for the attack, the fifth in Britain this year, but London's Metropolitan Police said that claim could not be verified.
