TYNGSBOROUGH — A homemade incendiary device ignited while hanging from high-powered electrical wires in this Merrimack Valley town Wednesday, setting off a brush fire along a local road and sparking an investigation into how the object and several others wound up fastened to an important part of the power system.
Federal, state, and local authorities Thursday said they could find nothing to suggest the devices were installed as part of a terror plot. But they said the incident, which involved objects resembling pipe bombs, had targeted a key electrical link between Canada and the Northeastern United States.
“I can’t think of any other reason why somebody would want to do that, other than a sinister reason,” said Peter F. Kowenhoven, assistant special agent in charge at the FBI’s Boston office, which is leading the investigation.
He said authorities have not determined why the site was targeted but added officials were investigating the possibility that the suspect was trying to damage the wires or start fires.
The devices were discovered about 3 p.m. Wednesday, when Tyngsborough firefighters began battling a blaze behind Locust Avenue. Firefighters noticed the cylindrical devices hanging from the lines and at first suspected vandalism.
Law enforcement officials arrived, joined by crews from National Grid, which operates the power lines. The devices were activated by hand, Kowenhoven said. Officials emphasized they were not bombs.
“An incendiary device is one that ignites and causes extreme heat and fire,” Kowenhoven said. “It does not explode and go outward.”
By Thursday morning, authorities said, the devices had been disabled.
Only one of the devices was working when investigators discovered them, and law enforcement emphasized Thursday afternoon the incident did not pose a threat to the public.
Investigators would not reveal how many objects they found and referred further questions about the power lines to National Grid.
In a statement, the utility said its transmission system “is secure, operating normally and there is no effect on service to customers.” Spokeswoman Danielle Williamson declined to comment further about the risk posed by the devices.
“National Grid is working with law enforcement authorities on this issue,” she said in the statement.
Tyngsborough Police Chief Richard Howe noted the devices were hung in a hard-to-reach area. He said it would “take a considerable effort to get up as high as they did in this instance.”
“It’s not a place that you would pass through,” he said. “You could walk to it, it takes a little time. But it’s difficult terrain.”
Officials said they had a theory about how the devices were put in place but declined to share it.
Investigators remained at the scene into Thursday afternoon, looking for any clues.
State Police joined with the state fire marshal’s office to offer a reward of up to $5,000 for help in solving the case.
They asked anyone with information to call 1-800-682-9229.
Kowenhoven said the FBI had previously encountered devices that bore similarity to those found in Tyngsborough. He said the FBI has taken the objects to a laboratory, where specialists will examine them to see if they bear characteristic “signatures.”
Kowenhoven said the devices were “metal cylinder objects similar to a pipe bomb in structure.”
The agency has notified other law enforcement agencies and utilities nationwide.
Kowenhoven said investigators are “looking at numerous individuals,” but had not made any arrests.
Whoever set up the devices will face significant consequences, Howe, the Tyngsborough police chief, said.
“It’s a serious incident, a serious event,” he said. “If it was a prank, it was certainly a serious one – with serious repercussions.”
Andy Rosen can be reached at andrew.rosen@globe.com. Follow him on Twitter at @andyrosen.