As it happened: Boston Marathon explosions

Key Points

• Two explosions near the finish line of the Boston Marathon - the oldest and most prestigious race of its kind in the US - have left at least three people dead and more than 100 injured
• The road was strewn with debris, and bloodied runners and spectators were treated at the scene; Boston's police commissioner urged city residents to stay indoors
• US President Barack Obama said it was not known what caused the blasts but vowed any group found to be responsible would feel the "full weight of justice"