LONDON — A van drove into a group of pedestrians early Monday near a mosque in London, killing one person and injuring 10 in what the mayor called a “horrific terrorist attack” that struck Muslims as they finished prayers.

The Metropolitan Police confirmed that the case was being investigated as a possible act of terrorism. The driver of the van, a 48-year-old man, was arrested after bystanders kept him from fleeing, the police said in a statement.

One man was pronounced dead at the scene. Eight pedestrians were taken to three separate hospitals, and two were treated at the scene for minor injuries, the police said.

The mayor, Sadiq Khan, acknowledged that the situation was still unfolding, and he urged Londoners to remain calm and vigilant. “While this appears to be an attack on a particular community,” he said, “like the terrible attacks in Manchester, Westminster and London Bridge it is also an assault on all our shared values of tolerance, freedom and respect.”

The British prime minister, Theresa May, said that she would lead an emergency meeting later Monday about the case. “All my thoughts are with the victims, their families and the emergency services on the scene,” she said.