Among the five American troops killed this week during a possible friendly fire airstrike in Afghanistan were a soldier from northern Illinois who deployed a month after his father died and a soldier from Ohio who was engaged to be married, representatives of their families say.
Pentagon spokesman Rear Adm. John Kirby said the five American troops were killed Monday "during a security operation in southern Afghanistan." Officials said an airstrike was called in after the unit was ambushed by the Taliban.
"The casualties occurred during a security operation when their unit came into contact with enemy forces," a statement from NATO's International Security Assistance Force read Monday. "Tragically, there is the possibility that fratricide may have been involved. The incident is under investigation. Our thoughts are with the families of those killed during this difficult time."
If confirmed, it would be one of the most serious cases involving coalition on coalition friendly fire during the nearly 14-year Afghan war.
A senior U.S. defense official told Fox News early Tuesday that the troops were killed when they requested air support from a B-1 bomber.
One of those killed was Aaron Toppen, 19, family spokeswoman Jennie Swartz told The Associated Press from the family's Mokena home, about 40 miles southwest of Chicago. Swartz said representatives from the U.S. Army came to the door of Toppen's mother, Pam Toppen, in the middle of the night to deliver the news.
"Aaron was predisposed to serve. He was very keen to be in the military," his uncle, Jack Winter, said. "He was quite proud to be there."
Military representatives also went to the home of Justin Helton's parents in Beaver, Ohio, early Tuesday to inform them of their son's death, a relative said.
Mindy Helton said her cousin specialized in dealing with explosives and was based out of Fort Bragg, North Carolina.
Justin Helton, 25, had been in Afghanistan about two months and was engaged to be married, she said. He had been in the Army since 2010.
"He was a great boy, so full of life and outgoing," she said. "He loved hunting and the outdoors."
As Toppen's family and friends gathered at the light blue home, Winter described the high school graduate as a caring and funny man who was "something somewhat rare in youth culture today. ... In a word, I would summarize what he had as 'class,'" Winter said. "So rarely now do you see somebody like that who truly does have class who's polite, humble, loyal, who's a kind-hearted soul, generous."
It was the second death of a loved one for the family this year. Toppen was set to leave for Afghanistan in February, but his gravely ill father died that month and he stayed for the funeral. He deployed in March.
Toppen was a graduate of Lincoln-Way East High in Frankfort, Illinois, and loved the outdoors, especially fishing. Family members at the home — where friends continued to stop by and bring food Tuesday evening — circulated a picture of Toppen as a young child sitting next to his father in a fishing boat.
Military members provided few details of the attack to the family, Winter said.
"A military representative came to my sister's home ... and broke her heart," Winter said. "It just tears your world apart. That's the situation my sister is in."
Toppen was the youngest of three children.
The other three victims have not yet been identified.
The only U.S. troops now involved in combat operations are usually Special Operations Forces that mentor their Afghan counterparts. They often come under fire and are responsible for calling in air support when needed. Because of constraints placed by outgoing Afghan President Hamid Karzai, such airstrikes are usually called "in extremis," or when troops fear they are about to be killed.
The Taliban claimed responsibility for Monday's ambush in Zabul.
A Taliban spokesman, Qari Yousef Ahmadi, said a battle took place between foreign troops and Taliban fighters in the Arghandab district, and a "huge number" of NATO soldiers were killed or wounded in the fighting. The Taliban often exaggerate their claims.
Separately, a NATO statement said a service member died Monday as a result of a non-battle injury in eastern Afghanistan.
The deaths bring to 36 the number of NATO soldiers killed so far this year in Afghanistan, with eight service members killed in June.
The insurgents have intensified attacks on Afghan and foreign forces ahead of the country's presidential election runoff Saturday. Officials are concerned there could be more violence around the time of the vote, although the first round in April passed relatively peacefully.
Casualties have been falling in the U.S.-led military coalition as its forces pull back to allow the Afghan Army and police to fight the Taliban insurgency. All combat troops are scheduled to be withdrawn from the country by the end of this year.
Fox News' Jennifer Griffin and The Associated Press contributed to this report.