One person has died, one person is unaccounted for and at least 10 are injured following an explosion at a U.S. Steel plant near Pittsburgh, Allegheny County Police Assistant Superintendent Victor Joseph said at a press conference Monday afternoon.

Officials are still working to determine the cause of an explosion that rocked a steel plant outside Pittsburgh, leaving two dead and 10 injured.

At least one person has died, and one person remains unaccounted for, while at least 10 people have been injured following multiple explosions at the U.S. Steel Clairton plant.