London Marathon Chief Executive Nick Bitel:
We are deeply saddened and shocked by the news from Boston.
Our immediate thoughts are with the people there and their families. It is a very sad day for athletics and for our friends and colleagues in marathon running.
Our security plan is developed jointly with the Metropolitan Police and we were in contact with them as soon as we heard the news.
Metropolitan Police chief Superintendent Julia Pendry:
We will be reviewing our security arrangements in partnership with the London Marathon.