A bomb hidden in a garbage container exploded Saturday in the north-eastern US state of New Jersey along the planned route of a 5-kilometre charity run sponsored by the US Marines.
There were no injuries, a spokesman for the prosecutor's office in Seaside Park, New Jersey, told CNN. The bomb, which was described as a pipe-bomb-type device, was wired to others that failed to explode.
The bomb went off at 9:35 am (1335 GMT) on the route of the race in which 3,000 runners were to participate.
"It's obvious it was meant to affect the run," said the spokesman, Al Della Fave, adding that the only reason no one was hurt was the start of the race had been delayed by a high turn-out for the event.
If not for the delay "there probably would have been a good number of people running past" at the time of the explosion, he said.
Federal investigators with the FBI have joined local law enforcement agencies in the investigation, Della Fave said. Many of the runners were members of the US armed forces.
A message on the race's official website said the event had been cancelled "due to an unidentified suspicious backpack found at the race site."
Della Fave said authorities had evacuated several blocks of Seaside Park, located along New Jersey's Atlantic Coast. The boardwalk area also was evacuated and placed on lockdown while a search was conducted.