British authorities arrested an 18-year-old man in Dover on Saturday as part of the ongoing investigation into Friday’s train bombing in London, which left dozens of people injured.
“We have made a significant arrest in our investigation this morning,” said Neil Basu, the U.K.’s senior national co-ordinator for counter terrorism policing, according to Reuters.
Dover is port city in the southern part of the country, where people frequently use passenger ferries to sail to France.
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The arrest comes one day after Prime Minister Theresa May said the country’s threat level had been raised to “critical,” meaning an additional attack could be imminent.
British authorities previously raised the threat level to critical in May after a man killed 22 people at an Ariana Grande concert in Manchester.
Basu said the threat level would continue to remain at critical following Friday’s bombing at London’s Parson’s Green train station, which left 30 people injured.
British authorities announced they were treating the incident as a terror attack.
President Trump was quick to condemn the attack on Twitter, saying it was carried out “by a loser terrorist.”
May responded to Trump’s characterization, saying it is never helpful for someone to speculate on an ongoing investigation.