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EAST CHICAGO — The FBI is leading an investigation into Wednesday's explosion inside a U.S. post office building that sent one postal worker to the hospital.

The female employee was transported to St. Catherine Hospital in East Chicago, according to FBI Special Agent Bob Ramsey.

She suffered minor injuries according to an official on scene.

Federal agents, along with local law enforcement and firefighters, were on scene at the federal building, 901 E. Chicago Ave., according to the city's fire chief, Anthony Serna.

A ﬁre official at the scene confirmed there was at least one explosive device.

The Porter County's bomb squad was on scene with a bomb disposal robot.

At least two bomb-sniffing dogs with the Lake County Sheriff's Department were on the scene as well.

The fire department received the call of a possible explosion at 5:59 p.m., Serna said. At least one employee was inside the building at the time of the explosion.

About 8:30 p.m., bomb squad officials could be seen huddled outside the post office building. As of press time, no official had yet entered the building.