U.S. President Barack Obama says the United States will find out who was responsible for Monday's bomb attacks in Boston.
At least three people were killed and more than 140 injured, after two bomb blasts went off near crowds of spectators at the finish line of the prestigious Boston Marathon.
A third blast rocked the JFK library several kilometres away.
The blasts occurred about two hours after the first of the race's 23 000 runners had crossed the finish line.
Obama says they will find out who's responsible and hold them to account..
Meanwhile, a group of 28 South Africans went over to compete in the marathon.
Two of them were injured in the twin blasts.
