British police have made a "significant" arrest in the urgent manhunt for suspects a day after the London subway blast that injured more than two dozen people, authorities say. Police say that an 18-year-old man was arrested by Kent police Saturday in the port of Dover on the English Channel, the AP reports. He is being questioned under the Terrorism Act. Dover is a major ferry port for travel between Britain and France. "We have made a significant arrest in our investigation this morning," Deputy Assistant Police Commissioner Neil Basu said. But he warned that the investigation was ongoing and the terrorist threat level remains at "critical," meaning a government task force believes another attack is imminent.
Basu's comments suggested that other dangerous suspects may still be at large. The 18-year-old suspect hasn't been charged or identified. Police say he will be brought to a south London police station for more questioning. Police haven't said if he is suspected of planting the bomb or if he played a supporting role in a possible plot. Prime Minister Theresa May said raising the threat level to its highest point was a "proportionate and sensible step." Police called on the public to be vigilant. Armed police will be joined by soldiers at public places in London Saturday to deter further attacks. (May and the London Metropolitan Police have described President Trump's tweets about the attack as "unhelpful.")