(Reuters) - One employee was killed and four others were injured in an explosion at a U.S. Army ammunition plant in Independence, Missouri, on Tuesday, a spokeswoman for the Joint Munitions Command said.

A spokeswoman for the Munitions Command, which manages ammunitions installations for all branches of the U.S. military, said the four injured workers were evaluated at the scene and declined further treatment.

An earlier statement had said that three people were taken to a local hospital for evaluation. The spokeswoman, Justine Barati, said that statement had been in error. Barati did not identify the person killed in the explosion.

Barati said the blast took place at about 1 p.m. central daylight time (2 p.m. EDT) in a primer mixing cell at the Lake City Army Ammunition Plant. A mixing cell is a building area where the components of munitions are mixed together.

The scene was secured and rendered safe by U.S. Alcohol Tobacco, Firearms and Explosives agents, and an investigation could determine what caused the explosion, Barati said.

The facility was closed for the remainder of Tuesday, and employees were told to check with managers before returning to work on Wednesday.

The Lake City Army Ammunition Plant, which opened in 1940, makes small-caliber munitions and operates as a North Atlantic Treaty Organization test center.

Independence, Missouri, is about 10 miles east of Kansas City.