Four additional attacks, all involving two teenage boys on a scooter, or moped, took place in rapid succession in neighborhoods nearby, with the assailants spraying acid in the faces of other scooter riders in an apparent attempt to steal their vehicles, the police said. They succeeded in stealing only two scooters during the spree, the police said.

All of the victims were men, ranging in age from 24 to 52, and there was no indication that the assaults were hate crimes. “These are hideous offenses and must have been very frightening for all of the victims,” Chief Inspector Ben Clark said. “I’m aware of rumors circulating that the victims were all food delivery riders set up in advance of the attacks. This is not the case. All victims were riding mopeds at the time of the attacks, but were from a variety of backgrounds.”

The police said the teenagers had been arrested on suspicion of robbery and of causing grievous bodily harm, and appealed for witnesses and anyone with footage of the attacks to come forward. All five victims were treated in an East London hospital, and at least four of them remain hospitalized, the police said.

The Metropolitan Police have said that acid attacks are on the rise in the British capital, with 458 reported last year, nearly double the total of the previous year. In a radio interview with LBC, the commissioner of the Metropolitan Police, Cressida Dick, called the attacks barbaric. “I don’t want people to think this is happening all over London all the time. It really is not,” she said. “But we are concerned, because the numbers appear to be going up.”

The British government began talking to the police, government officials and retailers this month about the feasibility of banning some acids, a process that would be complicated by the fact that they are commonly found in household products like drain cleaner and bleach.