Pennsylvania State Police, the FBI, and the ATF are investigating another mystery explosion in Upper Bucks County.

The latest blast occurred about 1 p.m. Thursday on Brick Tavern Road near Allentown Road in Milford Township and apparently was triggered by a John Deere tractor mower cutting grass bordering the roadway. No injuries were reported.

The explosion created a crater that was about two feet wide and two-and-a-half inches deep, 6ABC reported.

>> READ MORE: Upper Bucks residents desperate for answers as feds probe mysterious late-night explosions

Authorities have been investigating a series of more than 20 explosions that have been occurring in rural parts of Bucks County since early April. The blasts have typically occurred between the hours of 1 a.m. and 4:30 a.m.

Special Agent Charlene Hennessy, a spokeswoman for the Bureau of Alcohol, Firearms, Tobacco, and Explosives, said Friday that no "explosive device or evidence of an explosive device" was recovered from the site of Thursday's blast, despite what some residents reported to media outlets.

She deferred further comment to Trooper Marc Allen, the public information officer for the state police's Dublin Barracks. Allen did not return a request for comment.

On June 7, federal authorities responded to a report of another explosion along Brick Tavern Road. After that blast, all an FBI spokeswoman would say was that investigators from the agency had assisted local police at the scene.

The lack of information from both federal and local investigators frustrated Richard Bash, who lives not far from the field where Thursday's explosion was reported.

"It's bewildering to me that someone can do this all this time and no one can find any clues," he said.

Bash said Thursday's explosion was the second blast in the area this week, after one that occurred early Monday. The booming explosions have been going off near his home since the spring, usually around 4 a.m.

The Vietnam War veteran likened the sound to a mortar going off.

"It's almost enough to give you PTSD," he said.

Bash said Thursday's explosion was the first to happen during daylight hours, and was powerful enough to blow a two-foot hole in the ground.

He said state police investigators questioned him Thursday about a theory he has — that the blasts were coming from a nearby campground — but they later told him that they found nothing to support that.

"But meanwhile, we all have to live with this," he said.