Police and security chiefs on Tuesday reviewed security arrangements for the London Marathon after organisers said the race would go ahead this weekend in the wake of the bombings which caused carnage at the Boston Marathon.
Sports Minister Hugh Robertson said he was "absolutely confident" that the London race could be kept safe on Sunday.
Two explosions during the Boston race on Monday killed three people and left many more with horrific injuries. The FBI said it was treating the bombs as a "potential terrorist investigation".
At least 36,000 runners will take part in the London Marathon, with the route taking in some of the best-known landmarks in the capital including the Houses of Parliament, Buckingham Palace and Tower Bridge.
The Boston bombings are a new security headache for British authorities, already on alert for the funeral with full military honours of former prime minister Margaret Thatcher in London on Wednesday.
Home Secretary Theresa May has been briefed on the bombings by senior Scotland Yard officers and head of MI5 Jonathan Evans.
Robertson said: "These are balance of judgments but we are absolutely confident here that we can keep the event safe and secure.
"I think this is one of those incidents where the best way to show solidarity with Boston is to continue and send a very clear message to those responsible."
London Marathon chief executive Nick Bitel said the race would go ahead but underlined the impossibility of securing the entire 26.2-mile (42-kilometre) route.
"We will not be cancelling. What we are doing, we are reviewing," he told BBC radio.
"You look at what has occurred, if there are steps we can take to increase security and all sorts of measures one could deploy.
"We run through the city. When you have an event of any nature -- a marathon, parade... it's only as safe as the city itself. If it's not held in a stadium you can't do a lockdown like you may do in a building."
[Image via Agence France-Presse]