Security for the London Marathon on Sunday will be reviewed following the explosions in Boston, the Metropolitan Police have said.
The route passes some of the nation's most recognisable landmarks and organisers said they would assess safety arrangements for the event following the tragic scenes that marred the finish line in Boston.
Chief Superintendent Julia Pendry, the event commander for the marathon, said they would review security for the event, which draws spectators from all over the world.
She said: "A security plan is in place for the London Marathon. We will be reviewing our security arrangements in partnership with London Marathon."
The London race's chief executive, Nick Bitel, said today was "a very sad day for athletics and for our friends in marathon running".
Mr Bitel added: "Our security plan is developed jointly with the Metropolitan Police and we were in contact with them as soon as we heard the news."
The London Marathon is the world's largest marathon and attracts half a million spectators each year.
The flat and fast course, starting in Blackheath and finishing in front of Buckingham Palace, takes in some of the capital's top tourist sights including Tower Bridge, and Canary Wharf - one of the largest single business developments in the world.
Runners also pass Big Ben and Parliament Square.
The event first ran in 1981, and Sunday's will be the 33rd race.