MOKENA – Pam Toppen's last words to her son were "I love you."

Toppen's 19-year-old son, Aaron Toppen, was among the five troops killed during an apparent friendly-fire incident in southern Afghanistan Monday. Pam Toppen stood just outside her Mokena home Tuesday to speak to the media about her only son, with an American flag hanging from the house in the rain and a "Military Mom" flag in the front yard.

"(I said) I love him and I can't wait to hear about (his mission) when you come back," she said.

Aaron Toppen's uncle, Stephen White, former chief judge of Will County, called Toppen "an incredible human being," earlier in the day.

"He went for all the right reasons. His family had the 'Military Mom' flag in the yard. They are very proud of him," White said.

A family spokeswoman told the Associated Press that Toppen was among the five troops killed during a friendly-fire incident this week in Afghanistan.

Jennie Swartz said that Army officials informed the family that Toppen was among those killed Monday. She says Army officials came to his mother's home in Mokena overnight.

On Tuesday, family and close friends came to the house as the news of Toppen's death got around, said Ryan Gleason of Frankfort.

Gleason had been friends with Toppen. He described Toppen as very patriotic and someone who who wanted to serve in the military since he was a kid.

"It's something he felt he should do," Gleason said. "He had that honor, had that duty. That's a debt we can't repay."

He described Toppen as someone who "would give his shirt straight off his back for you." The two of them would look for people to help during bad weather, Gleason said. "We had pickup trucks," he said, "and in many instances he would help people stuck in the mud and snow."

A woman named Amanda Gralewski, who identifies herself as the sister of Aaron Toppen, stated on her Facebook page that her brother was among those killed in the attack.

"At midnight last night my mom's doorbell rang and we received the news that my little brother was one of the five involved in friendly fire in Afghanistan," she wrote on her Facebook page. "My brother lost his life doing what he always wanted to do since he was a little boy. He's my biggest hero and the bravest man I know."

Gralewski noted in her Facebook post that their father died in February. She wrote that she appreciated those who have reached out to her, and asked that "everyone please say a prayer."

Toppen was a 2013 graduate of Lincoln-Way East High School.

"Our thoughts and prayers go out to the family," Lincoln-Way Community High School District 210 Superintendent Scott Tingley said. "For someone of Aaron's age, this is a very tragic event."

Toppen was one of five American troops killed in an apparent coalition airstrike in southern Afghanistan, officials said Tuesday, in one of the worst friendly fire incidents involving United States and coalition troops since the start of the nearly 14 year war.

The U.S.-led international coalition said the service members were killed in an apparent friendly fire incident, which an Afghan official said was an airstrike in southern Zabul province. A statement said all five soldiers died on Monday but did not give further details.

"Five American troops were killed yesterday during a security operation in southern Afghanistan. Investigators are looking into the likelihood that friendly fire was the cause. Our thoughts and prayers are with the families of these fallen," Pentagon spokesman Rear Adm. John Kirby said.

If confirmed, it would be one of the most serious cases involving coalition-on-coalition friendly fire during the war.

"The casualties occurred during a security operation when their unit came into contact with enemy forces. Tragically, there is the possibility that fratricide may have been involved. The incident is under investigation," the coalition said in an earlier announcement.