Organisers of this weekend's London Marathon insist the event will go ahead as planned despite the fatal bomb attacks in Boston last night.
Three people died and at least 130 more were injured after two explosions rocked the finish line of the US race yesterday.
The incidents come six days before the London race, which attracts tens of thousands of runners from around the world, and organisers confirmed it would still go ahead - although talks are now ongoing with police about increasing security on the 26-mile route.
"We will not be cancelling, what we are doing, we are reviewing," Nick Bitel, chief executive for the race, told the BBC.
"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."
The Metropolitan Police confirmed they would be reviewing security for the event in the wake of the explosions in Boston.
"A security plan is in place for the London Marathon," said Chief Superintendent Julia Pendry
"We will be reviewing our security arrangements in partnership with London Marathon."
However Joel Laine, head of the Paris Marathon which was held earlier this month, admitted he feared the explosions would have a chilling effect on the runners scheduled to compete in London.
"There will be without doubt a climate of suspicion for a good while surrounding these type of events," he said.
"I am thinking notably of the London Marathon. "I am thinking of the anxiety this will instil in the competitors and their families."
The Boston Marathon is the oldest annual marathon in the world, first organised by the Boston Athletic Association in 1897 in the wake of the first modern-day marathon competition at the 1896 Olympics.
Nowadays the event is one of six World Marathon Majors, attracting elite racers from around the world as well as thousands of recreational runners and hundreds of thousands of spectators. More than 25,000 runners were registered for this year's event.
The explosions in Boston occurred close to the finishing line at around 3pm local time (11pm GST) yesterday, after the elite race had finished. Lelisa Desisa of Ethiopia won the men's race with Rita Jeptoo winning the women's.
The explosion took place as runners were still on the course, with those yet to reach the finish being held by police around the 26-mile mark.
Distance running greats Haile Gebrselassie and Paula Radcliffe were among those stunned by the blasts.
"Horrified to hear news of bomb explosion near Boston marathon finish," Radcliffe said on Twitter before the extent of the damage was known.
"Situation looks awful, thoughts with everyone," the fastest women's marathoner in history added later. "There are some very sick people out there, who would do something like this?"
Ethiopia's Gebrselassie deplored what marathon organisers said was a bomb attack, although law enforcement officials did not immediately confirm the cause of the explosions.
"Running brings people together, but what just happened in Boston is terrible," he said on Twitter. "My thoughts are with everybody in Boston."
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