A package exploded and injured one worker at a FedEx mail distribution facility in near San Antonio, Texas, this morning, prompting the FBI to send agents there to determine any connection to a series of bombings this month in Austin, officials said.
The explosion occurred about 12:30 a.m. at a FedEx facility in the San Antonio suburb of Schertz, about 65 miles southwest of Austin, where two men were injured Sunday night in the fourth bombing in 17 days to rock the Texas capital.
A medium-sized box containing nails and metal shrapnel exploded on a conveyor belt, according to police, who spoke with ABC San Antonio affiliate KSAT-TV.
Jim McClusky, a spokesman for FedEx, confirmed in a statement to ABC News that "a single package exploded" and that one worker was treated for minor injuries.
The injuries to the worker were "possibly from the sound of the device going off," Lt. Manny Casas of the Schertz Police Department said.
The worker was treated at the scene and did not have to be hospitalized, officials said.
There were 75 people in the building at the time of the explosion.
Police said they "hope" this is an isolated incident and do not know of any connection to the Austin bombings.
Austin Police Chief Brian Manley said investigators from his department, the FBI and the federal Bureau of Alcohol, Tobacco, Firearms and Explosives were working to determine whether the explosive is the work of a serial bomber or bombers who have terrorized Austin since March 2.
"I want to continue to remind our community to pay close attention to any suspicious device whether it be a package, a bag, a backpack or anything that looks out of place, do not approach it. Call 9-1-1 immediately. Also remember do not move, touch or open unexpected/suspicious packages," Manley said in a statement this morning.
Manley said Monday at a news conference on the Austin explosions, "clearly we are dealing with a serial bomber."
It is going to take a considerable amount of time before any post-blast investigation can occur at the Schertz FedEx facility, a law enforcement source told ABC News.
The site is complicated and potentially dangerous to render safe, with other FedEx packages of unknown contents all over. Authorities will have to move slowly and methodically to process the complex scene, the source said.
Austin residents have been on edge for a month after the series of bombings that killed two and injured four people. The first three bombings were packages, apparently hand-delivered and left on porches of homes before exploding when picked up by residents, police said.
The fourth explosion took place Sunday night. Two men, ages 22 and 23, were injured in that blast, which was caused by a device using a tripwire on a sidewalk in the Travis Country neighborhood of Austin.
ABC News' Jack Date contributed to this report.