Organizers for Sunday's London Marathon are reviewing security arrangements after the bombings at the Boston Marathon on Monday.
London Marathon Chief Executive Nick Bitel said in a statement that "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.
"The London Marathon fully expects at this stage that the race will go ahead as planned on Sunday, although we are continuing to review security with the Metropolitan Police.