British police say they are reviewing security plans for Sunday's London Marathon, the next major international marathon, because of the explosions that hit the race in Boston.
Thousands of people compete in the London Marathon every year, thronging the city's streets. London is also considered a top target for international terrorists.
It was not yet immediately clear what caused the blasts in Boston.
A London Metropolitan Police spokesman confirmed Monday that police are working with marathon officials to review security plans for Sunday's event.
The London race's chief executive, Nick Bitel, expressed shock and sadness about the situation in Boston, saying "it is a very sad day for athletics and for our friends in marathon running."