LONDON — As the police in the United States hunted down and traded fire with the men suspected in the Boston bombings, Scotland Yard said on Friday that it had increased the number of officers assigned to guard the London Marathon on Sunday by several hundred to reassure runners and spectators of their safety.

The London event, one of the world’s biggest, with tens of thousands of competitors and many more onlookers, is the first major international race of its kind since Monday’s bombings in Boston killed three people and wounded more than 170. The 37,000 runners include many stars, like the British Olympic gold medalist Mo Farah, who is running only the first half of the race.

The finish line of the event lies within sight of Buckingham Palace on the broad avenue called The Mall. At the starting line, runners are to pause for a 30-second silent commemoration of the victims in Boston, and the organizers say they will hand out black armbands for contestants.

Chief Superintendent Julia Pendry, who is in charge of the policing of the London Marathon, said additional deployments would increase the number of officers by 40 percent compared with last year.