London Marathon officials ruled out cancelling the event, in which approximately 37,500 people will run 26.2 miles from Blackheath, south-east London to the Mall, with an estimated 500,000 people lining the streets to watch them.
Met police chief superintendent Julia Pendry said that although a well-oiled security plan was already in place, it would be immediately revisited in co-operation with organisers.
Security is expected to be stepped up for the event, one of six marathons that form the World Marathon Majors series, along with Boston and four others.
"A security plan is in place for the London Marathon. We will be reviewing our security arrangements in partnership with London Marathon," said Pendry.
London Marathon chief executive Nick Bitel said he had made contact with the police as soon as news of the two explosions at the finish line of the Boston event, which attracts more than 26,000 participants, filtered through.
"We are deeply saddened and shocked by the news from Boston. Our immediate thoughts are with the people there and their families," said Bitel.
"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."
London mayor Boris Johnson said he was shocked by the events at the Boston Marathon, which is the world's oldest. Given its nature, securing the 26.2 miles of the marathon course was one of the biggest fears of the police and organisers ahead of the London Olympics last year.
The popularity of mass participation marathons has soared around the world in recent years and in Britain the sport is one of the few to increase the number of people taking part.
Marathon tourism has also taken off, with many keen British runners travelling to Boston, New York, Paris and Tokyo to compete abroad. Entry lists for the Boston marathon showed that 374 British runners and over 100 Irish runners had registered to take part.
Jez Hughes, a British runner who took part in the Boston event, told Sky News: "We heard a massive explosion. I said to my wife I thought it sounded like a bomb and she thought it was fireworks. Five seconds afterwards there followed another explosion.
Hughes, who finished his race half an hour before the explosion, said: "There was nothing we could do."
UK Athletics said that none of its elite runners had taken part in the race. Ross Murray, who ran in Sunday's one-mile invitational event was said to be "absolutely fine".
All of the elite runners were believed to have finished and were back at their hotel when the bombs went off. By the time the explosions happened, all of those who were finishing would have been fun runners and those completing the course for charity.
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