Two bombs went off within seconds of one another Monday near the finish line for the Boston Marathon. At least three people died and more than 100 others were injured in the attack.
Ban described the bombings as "senseless" acts of violence that was "all the more appalling for taking place at an event renowned for bringing people together from around the world in a spirit of sportsmanship and harmony."
There have been no claims of responsibility in the attack. Security studies Professor at King's College, London, Peter Neumann told The Daily Telegraph the attacks bore the hallmarks of "amateurish right-wing or amateurish al-Qaida" operations.
Planners of the London Marathon, scheduled for Sunday, said the event would go on as planned but with heightened security precautions.
Juliette Kayyem, a counter-terrorism specialist at Harvard's Kennedy School of Government, told The Boston Globe the attack was "probably home-grown."
The attacks coincided with a series of historic events in the United States, ranging from the deadline for tax filing to Patriots Day in Massachusetts. Friday marks the 18th anniversary of the bombings in Oklahoma City and Saturday marks the 14th anniversary of the school shootings in Columbine, Colo.
Russian President Vladimir Putin offered support to U.S. investigators Tuesday. Russia hosts the Winter Olympic Games next year and is scheduled for a series of world athletic competitions this year.