A U.S. KC-135 refueling aircraft went down in western Iraq, taking the lives of six service members, Reuters reports. The names are being withheld until relatives are notified.

The KC-135 Stratotanker refuels jets midflight.

What happened in the air over Iraq

U.S. Central Command says the tanker crashed after an incident involving another aircraft in what it called friendly airspace. That second plane landed safely. The military says the loss was not caused by hostile fire or friendly fire, according to Reuters. Still, the sky over Iraq remains crowded and tense.

Al Jazeera reported that an Iran-backed Iraqi armed group claimed responsibility, even as the U.S. military publicly rejected hostile fire as the cause.

The crash site was reported near Turaibil, close to Iraq’s border with Jordan.

Why the KC-135 matters in war

The aircraft was not a fighter. It was the plane that keeps fighters in the air. The KC-135 Stratotanker refuels jets midflight, which lets combat aircraft stay on station longer and strike farther from base.

AP News reports that the aircraft has been in service for more than 60 years and is also used for medical evacuation and surveillance support. Its age has raised long-running concerns about durability, even after upgrades.

A recovery mission in a dangerous place

The crash site was reported near Turaibil, close to Iraq’s border with Jordan, CBS News reports. That matters because getting to a downed crew is never simple.

CBS reports that these recovery operations move fast and can place troops at risk as they try to secure survivors, recover the dead, and protect sensitive equipment. For the families waiting at home, the official details remain sparse.