A soldier from Mokena was among five American troops killed in an apparent coalition airstrike in southern Afghanistan, his sister said Tuesday.

Aaron Toppen, 19, died in what could be one of the worst friendly fire incidents involving United States and coalition troops since the start of the nearly 14-year war. Amanda Gralewski, his sister, confirmed his death for the Chicago Sun-Times.

She said a military chaplain and sergeant visited her mother’s home in the middle of the night to inform the family of Toppen’s death. Gralewski said she arrived before the military officials left and also spoke to them.

Gralewski said her brother died doing “what he wanted.” She said their grandfathers both served in the military — one in the Navy and one in the Army.

“Aaron was a funny, caring, loving kid,” Gralewski said. “He loved to fish. He loved his friends. He loved being outdoors. He loved his family. He would give the shirt off his back for anyone.”

Toppen left March 7 for Afghanistan, Gralewski said. He expected to leave a month earlier, she said. But she said their father, Ronald Toppen, died Feb. 7.

Now she said her family is suffering from a “double hit” of grief.

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 the southern Zabul province. A statement said all five soldiers died on Monday but did not give further details on the attack.

“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.

Contributing: Associated Press

Email: jseidel@suntimes.com

Twitter: @SeidelContent