The Boston Marathon came to a grim stop Monday (15.04.2013) after two explosions left at least three people dead and dozens injured. Two bombs were detonated near the marathon's finish line in what US authorities are treating as a coordinated terror attack. It would be the largest such incident in the US since the attacks on September 11, 2001.

Following the detonations, large plumes of smoke rose into the air near the finish line of the 42-kilometer race. Beneath the smoke, confusion and agony reigned among many of the race's tens of thousands of participants and spectators.

Spectators near the explosions described having heard and seen huge detonations. Some reported seeing individuals nearby lose limbs. Other victims were knocked by the blasts to the ground in scenes that have been called very bloody. The injured were transported by ambulance to hospitals, while some were treated in a tent originally set up to care for exhausted marathon participants.

After the two initial bomb blasts at around 3 p.m. local time, police and medics lined the streets. The first explosions came nearly five hours after the start of the race. There were no immediate claims of responsibility for the attacks, and authorities in the US have yet to confirm motives or groups behind the bombs.

Images of distress were captured around Boston. The East Coast city's marathon is among the most popular in the world, attracting hundreds of thousands of spectators. The city remained on edge Monday as initial reports came that further, undetonated explosives had been discovered in Boston. Those reports were later withdrawn.

The White House responded swiftly to the attacks. President Obama delivered a televised address in which he reiterated that those behind the explosions remain unknown but "will feel the full weight of justice." Security was beefed up around the White House in Washington after the bombs were reported.

The Boston Marathon routinely draws some 20,000 participants each year, with around 27,000 runners at the 2013 event. The 117th edition of the marathon began uneventfully, with the first rounds of finishers - including top athletes - completing the event long before the bombs were detonated. But many others had yet to finish the race when it drew to a tragic halt.

Police officers and bomb detecting dogs investigate near the finish line area a day after the bomb attack. Security authorities are poring over video and photographs from the widely-watched marathon for clues on who is responsible for the attack.

In Paris, French police patrol in front of the Eiffel Tower a day after the Boston bombing. France ordered police patrols to be stepped up and people were asked to be "vigilant as far as suspicious parcels or abandoned luggage are concerned."

As the US and Massachusetts flags flew at half staff in front of the Hancock building near the finish line in honor of the blast victims, organizers of upcoming marathons in London, Cologne and Berlin announced a review of their security arrangements.