(CNN) -- An explosion that went off in a garbage can Saturday morning in a New Jersey beach town likely was timed to disrupt a Marine Corps charity run, authorities said.
Three pipe-bomb-type devices wired together were found near the boardwalk in Seaside Park. No injuries were reported, and a four-block area was evacuated, authorities said.
An initial examination showed the devices were rudimentary, with some type of timer, and only one of them detonated, two federal law enforcement officials told CNN.
Al Della Fave, a spokesman for the Ocean County prosecutor's office, said he believes the blast was meant to affect the Seaside Semper Five race.
"If it was just a matter of minutes, in terms of difference, there would have been a good number of people running past that explosive device" because of its location along the race route, Della Fave said.
Registration problems at the starting line delayed the start of the race, which meant no one was near the garbage can when the explosion happened, a law enforcement official said.
"We were lucky," the official said.
Just after the explosion, Della Fave said, the area was placed on lockdown, and police deployed bomb detection dogs. He said no additional devices were found after the dogs completed their sweep.
"Until the bomb squad gives us the all-clear in terms of that garbage pail, we're going to keep that area closed off," he said.
It's not clear whether the motive was criminal or terrorist, Della Fave said, but "it's obvious it was meant to affect the run."
The FBI, the Bureau of Alcohol, Tobacco, Firearms and Explosives, the Joint Terrorism Task Force and local law enforcement are investigating, an FBI official said.
A race volunteer told CNN's Anne Woolsey that police and local law enforcement made the decision to shut down the race.
"It is a real shame that that charitable run that does so many great things for the Marines is now canceled," Della Fave said. "There's no word on when it will be rescheduled, but that's where we're at right now."
CNN's Evan Perez and Joe Sterling contributed to this report.