One U.S. postal employee was injured when a pipe bomb exploded at a post office in the Indiana State, the FBI said on Thursday.
The explosion happened on Wednesday evening at a U.S. post office branch in the city of East Chicago.
"We can confirm there was only one pipe bomb which injured a postal employee who was treated for minor injuries," the FBI said in a statement Thursday.
Investigators are still trying to ascertain if there are any terrorism links, added FBI, urging the public to offer tips.
Local firefighters said they believe the explosion came from a possible pipe bomb in a package.
The female employee, reportedly pregnant, was taken to a nearby hospital as a precaution.
East Chicago is a city in Lake County, Indiana, with a population of about 29,000. The city was named from its location east of Chicago, Illinois.