The names of two of the six US service members who died when the military refueling aircraft they were aboard crashed over Iraq last week were made public Saturday, revealing a father who had recently been promoted and a beloved son.

The Ohio air national guard said that three of the service members came from its 121st air refueling wing in Columbus, while a family from Birmingham, Alabama, confirmed that pilot Alex Klinner was killed in the crash.

The Pentagon, which has yet to formally identify the six service members, has said the loss of the KC-135 Stratotanker was not caused by hostile or friendly fire.

The family said that Klinner, 33, had recently been promoted to major and been deployed less than a week. His brother-in-law, James Harrill, said that Klinner leaves behind three small children: seven-month-old twins and a two-year-old son.

“It’s kind of heartbreaking to say: he was just a really good dad and really loved his family a lot – like a lot,” Harrill told the Associated Press.

“Over the past 24 hours my family has experienced an unimaginable loss,” Harrill said in a post on Instagram. “He was the kind of man who made everyone around him feel steady and safe. A devoted husband, an incredible father, and someone who lived with a quiet strength and humility that is hard to put into words.”

He added: “The grief is deep, but so is the pride. Alex served his country with courage and conviction, and the way he loved his family was even more extraordinary.”

The Ohio air national guard’s 121st air refueling wing said in a Facebook post late Friday that three of the dead were service members who served in the Columbus-based unit.

“We share in the sorrow of their loved ones, and we must not forget the valuable contributions these Airmen made to their country and the impact they have left on our organization,” according to the post.

Another service member who died in the crash has been named as Sgt Tyler Simmons of Columbus, Ohio, by his mother, Cheryl Simmons, who said she was making funeral plans for her son.

In a statement obtained by WCMH-TV in Columbus, Tyler Simmons’s family said it was saddened beyond measure to hear of the fatal crash.

“Tyler’s smile could light up any room, his strong presence would fill it. His parents, grandparents, family and friends are grief stricken for the loss of life,” they said.

US Central Command, which oversees the Middle East, has said the crash occurred in western Iraq on Thursday following an unspecified incident involving two aircraft in “friendly airspace”. The other tanker involved in the incident landed safely in Israel.

The crash brings the US death toll in Operation Epic Fury to at least 13 service members, with the seven others killed in combat. About 140 US service members have been injured, including eight severely, the Pentagon said earlier this week.

Defense secretary Pete Hegseth described the lost air crew as heroes.

“War is hell. War is chaos,” Hegseth said at a news conference on Friday. “And as we saw yesterday with the tragic crash of our KC-135 tanker, bad things can happen. American heroes, all of them.”

The KC-135 has been in service for more than 60 years. In civilian terms, it is the Boeing 707 passenger plane, retired from US passenger service in 1981. The tanker has been involved in several fatal accidents, most recently in 2013, in central Asia.

It is used for mid-air refueling but can also be deployed to transport wounded personnel during medical evacuations or conduct surveillance missions. According to the Congressional Research Service, the air force last year had 376 KC-135s, including 151 on active duty, 163 in the air national guard and 62 in the air force reserve.

While details of the incident are not yet public, questions are being asked about why the air crew are not believed to have been issued parachutes.

A 2008 news release from an air refueling unit said the air force was pulling parachutes from KC-135s, noting that it was statistically safer to stay with the aircraft, “especially when flying over enemy territory”.

“Removing parachutes from military aircraft may sound peculiar, but KC-135s are not like other aircraft,” the news release stated. “They seldom have mishaps, and the likelihood a KC-135 crew member would ever need to use a parachute is extremely low.”