Marathon organisers are not fazed by the Monday bombing of the Boston Marathon. They insist these annual sport events that draw thousands of international participants will go on as scheduled, but with tighter security measures to ensure the safety of marathoners.

On Monday, the organisers of the London Marathon said they will hold the race on Sunday, April 21, as originally scheduled.

"The best way for us to react is to push ahead with the marathon on Sunday, to get people on the streets and to celebrate it as we always do in London," BBC quoted British Sports Minister Hugh Robertson.

"There are balances 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," he added.

The London Marathon has 37,500 entries led by Mo Farah, Britain's double Olympic long-distance champion, who will run a half-marathon. Also running are three medalists from the London Games' men's marathon and Kenyan runners Wilson Kapsang and Patrick Makau.

Besides the Boston and London Marathons, there are also the ones organised by Tokyo, Berlin, Chicago and New York.

In the Sunday run, the participants will observe 30 seconds of silence before each of the three starts to show their solidarity with the Boston victims. They will also be encouraged to wear a black ribbon that comes with their race number.

"We are determined to deliver an amazing event that will focus on one of the core pillars of the London Marathon, which is to have fun and provide some happiness and a sense of achievement in a troubled world," The Guardian quoted race director Hugh Brasher.

Because of the Boston tragedy which killed 3 and injured 176 people, a social media campaign initiative asks London runners who cross the finish line would be encouraged to place their hands over their hearts as a show of solidarity with the Boston victims.

On Tuesday, law enforcement officials in the U.S. said the group behind the bombing probably used some kind of pressure cooker devices filled with metal, which explains the small pellets and sharp nail-like objects found on the explosion victims.

Athletes and sports officials also joined the world in condemning the bombing incident.

"What makes this incident so vile and its planning so incomprehensible is that marathons the world over are about selfless acts of human generosity. There can be no excuse, no cause which can justify these explosions in Boston which so sicken us all," The Guardian quoted International Association of Athletics Federations President Lamine Diack.

"A marathon is a special, almost magical event that unites different communities with one shared goal, and I am sure that this incident will serve to bring together all those who took part and all those who support such an event, with a common resolve," added International Olympic Committee President Jacques Rogge.