Official says soldiers were working on clearing supply routes of improvised bombs when one went off.
Four guardsmen, including one from Aurora, were killed in southern Afghanistan when a roadside bomb struck their vehicle, officials say.
A fifth soldier was injured.
Spc. Christopher Patterson, of Aurora, Staff Sgt. Jonathan Metzger of Indianapolis, Spc. Brian Leonhardt of Merrillville, Ind., Spc. Robert Tauteris Jr., of Hamlet, Ind., and Pvt. Douglas Rachowicz, of Hammond, Ind., were members of the 713th Engineer Company headquartered in Valparaiso.
Indiana Adjutant General Martin Umbarger said the officers were working on one of the more dangerous missions of clearing supply routes of improvised bombs.
One of the bombs hit the vehicle, killing Patterson, Metzger, Leonhardt, and Tauteris. Rachowicz sustained injuries and was airlifted to a U.S. military hospital in Germany.
"Their mission is to keep the major supply routes clear of all obstacles for the convoys," Umbarger said. "What that means is they're the first ones to go out and make sure the route can be used, so it's a very important mission -- but it's also extremely dangerous."
Indiana Gov. Mitch Daniels said he was informed of the men's deaths Saturday morning and that he's praying for their families.
"I had begun to hope that I had received the last such phone call, and cannot convey the sadness which it instantly brought," he said.
Umbarger said in a statement that he is "humbled and honored" by the courage of the nation's service members and said the sacrifices of the four men won't be forgotten.
"I would like to extend my deepest condolences to the families and loved ones of these brave citizen-soldiers," Umbarger said in a statement. "We will honor their sacrifice and always remember them."
Indiana National Guard: 713th Engineer Company