Lukeman extended condolences to the families of the victims. "Our first priority is to provide them support and we're doing that now," he said.
The Marine Corps said in a statement that it suspended all use of high-explosive and illumination mortar rounds that were in the same manufacturing lots as the ones that were fired in Nevada. The Pentagon suspended use of those rounds worldwide across all branches, not just the Marines.
The Marines were also considering a stop-usage order affecting the mortar tubes like the ones in the accident.
It was not immediately clear whether more than a single round exploded, a Marine Corps official said, speaking on condition of anonymity because the official wasn't authorized to speak about an ongoing investigation.
Eight men under the age of 30 were taken to Renown Regional Medical Center in Reno with injuries, such as penetrating trauma, fractures and vascular injuries. One of them died, five were in serious condition, one in was fair condition and another was discharged, said spokesman Mark Earnest.
The identities of those killed won't be released until 24 hours after their families are notified.
"We send our prayers and condolences to the families of Marines involved in this tragic incident," said the force's commander, Maj. Gen. Raymond C. Fox. "We mourn their loss, and it is with heavy hearts we remember their courage and sacrifice."
The rescue was complicated by the remoteness of the site, which is favored because the harsh geography simulates conditions in Afghanistan.
The 60mm mortar is a weapon that traditionally requires three to four Marines to operate, but it's common during training for others to observe nearby.
The mortar has changed little since World War II and remains one of the simplest weapons to operate, which is why it is found at the lowest level of infantry units, said Joseph Trevithick, a mortar expert with Global Security.org.