Officers, already on high alert for the funeral of former British Prime Minister Margaret Thatcher here tomorrow, have stressed that there is no credible threat to the London event.
"A security plan is in place. We will be reviewing our security arrangements in partnership with London Marathon," Metropolitan Police Chief Superintendent Julia Pendry, in charge of policing the London Marathon, said in a statement.
"The bombings in Boston are shocking, cowardly and horrific. We do have robust security measures in place, but given events in Boston it's only prudent for the police and the organisers of Sunday's race to re-examine those security arrangements," added London mayor Boris Johnson.
"We are deeply saddened and shocked by the news from Boston. Our security plan is developed jointly with the Metropolitan police and we were in contact with them as soon as we heard the news," said Nick Bitel, chief executive of London Marathon, which is expected to be competed by around 37,500 competitors.
More From This Section
An estimated 500,000 spectators are expected to line the streets to watch them run 26.2 miles from Blackheath, in the south-east of the capital, to the Mall in central London.
"This is one of those instances where the best way to show solidarity with Boston is to continue," he told BBC.
At least three people were killed and more than 100 injured by the blasts near the finish line of Monday's marathon in Boston, with 26,000 participants and thousands of spectators.