Officials from the sporting world say they were shocked, stunned and saddened by Monday's deadly blasts near the finish line of the Boston Marathon.
The president of the world governing body for track and field [IAAF], Lamine Diack, called it a "ghastly and cowardly attack" that "strikes at the very core of the freest of human activities." He added "what makes this incident so vile is that marathons the world over are about selfless acts of human generosity."
International Olympic Committee President Jacques Rogge said "a marathon is a special, almost magical event that unites different communities with one shared goal" and his "thoughts and those of all the Olympic Movement are with the victims."
The bombings resulted in the cancellation of Monday night's National Hockey League game in Boston, where the Bruins were to host the Ottawa Senators. Tuesday night's National Basketball Association game between the visiting Indiana Pacers and Boston Celtics also was canceled.
No other major U.S. sporting events were immediately called off.
Organizers of this Sunday's London Marathon - typically watched by half a million people - say that race will go on amid tighter security. Britain's sports minister Hugh Robertson said holding the event would be "the best way show solidarity with Boston.
Russian officials are promising tighter security measures for track and field's [IAAF] world championships in Moscow this August. Russian Sports Minister Vitaly Mutko described the Boston Marathon attack as "a grave signal."
Security already was being tightened at Major League Baseball stadiums and NBA and NHL arenas.
Indianapolis Motor Speedway spokesman Doug Boles said Monday's bombing would be a part of future meetings to review what precautions should be taken at the auto race in May that annually draws more than 350,000 spectators.