The Pentagon deployed elite commandos in response to the deadly ambush of a Special Forces team in Niger, fearing that one soldier who was missing at the time was alive and might fall into enemy hands, military officials said.

The commandos, with the secretive Joint Special Operations Command (JSOC), were deployed late on Oct. 4 after three U.S. soldiers and five Nigerien troops partnered with them were declared killed in action, said three officials, who had familiarity with the operation and spoke on the condition of anonymity because of its sensitivity.

Earlier in the day, French Mirage jets were dispatched from their base in Niamey, the Nigerien capital, along with French attack helicopters from Gao, in neighboring Mali. The U.S. request for assistance came after the troops notified their home base, an hour after the ambush began, that they were in trouble.

The jets took off within 30 minutes, and took another half-hour to reach the scene of the attack in the southwest corner of Niger near the border with Mali. They did not fire on what officials said was a confusing battlefield, to avoid hitting friendly forces. The helicopters, travelling more slowly and from farther away, took an additional hour to arrive.

It remains unclear whether the firefight was ongoing when the helicopters arrived, and when it became apparent that Army Sgt. La David T. Johnson was missing. His body eventually was recovered the evening of Oct. 6, after it was found by local Nigeriens and turned over to Nigerien authorities working with U.S. troops. It was not clear whether JSOC forces ever became directly involved in the search.

Two U.S. military officials said Johnson may have become separated from his unit in part because they were ambushed twice in succession, by militants believed affiliated with the Islamic State. That detail, first reported by NBC News, may explain the chaotic nature of the mission and the delayed call for assistance. Marine Gen. Joseph F. Dunford Jr., the chairman of the Joint Chiefs of Staff, said at a news conference Monday that the U.S. and Nigerien troops first faced enemy fire that morning, but may have initially thought the situation was under control.

Johnson's separation triggered declaration of what the military calls a DUSTWUN, which stands for "duty status whereabouts unknown," the officials said. Declaration of that status typically leads to an intense search for a missing service member. It is used when a commander suspects that a service member may be absent involuntarily, but does not think enough evidence exists to make a definitive determination, according to a U.S. military manual.

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Dunford appeared to allude to the deployment of JSOC members during his news conference Monday, saying that "national assets" were made available for the search. Dunford received a phone call from Marine Gen. Thomas D. Waldhauser, the chief of U.S. Africa Command, the night of the ambush — early the next morning, in Niger, which triggered approval for additional help, the chairman said.

Two U.S. military officials said it is unlikely JSOC would have deployed forces for the search if it was clear at the time that Johnson was dead. The concern, the officials said, was that the missing soldier could be captured alive.

"All of us were preparing at the time for PR support," said one U.S. military official, alluding to sensitive personnel recovery operations.

The deployment of JSOC in response to Johnson's disappearance was first reported by ABC News. It has not previously been reported that the military issued a DUSTWUN alert, or that commanders had concerns that Johnson was alive and potentially attempting to evade those who had ambushed his unit.

JSOC includes several of the military's most elite forces, including the Naval Special Warfare Development Group, better known as SEAL Team 6, and the Army's 1st Special Forces Operational Detachment-Delta, better known as Delta Force. It is not clear which force was assigned to help, or if more than one was involved.

Dunford declined to detail the specialized units involved.

"We have national assets and as soon as we had a missing soldier, we brought those assets to bear," the general said.

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Officials believe that those responsible for the attack were part of the Islamic State in the Greater Sahara, one of a number of small groups that began operating in Mali and Niger over the last two years. The Sahara group, led by Adnan Abu Walid Sahroui, a West African-born jihadist, pledged allegiance to and was officially recognized by the main Islamic State in late 2016. It is believed to have fewer than 60 adherents — although numbers and alliances fluctuate in the fluid situation in the sub-Saharan Sahel region — who operate mainly in the Niger-Mali border region.

The ambushed unit included 12 U.S. soldiers with the 3rd Special Forces Group, and deployed on a reconnaissance mission Oct. 3 while accompanied by about 30 Nigerien soldiers, Dunford said. They were attacked with small arms, rocket-propelled grenades and vehicles with weapons mounted on them outside the village of Tongo Tongo while trying to return to their base in Niamey, he said.

Johnson, 25, worked as a mechanic and was attached to the 3rd Special Forces Group team. His death has been at the center of a political fight in which President Trump has been accused of being disrespectful in a phone call last week to the soldier's pregnant widow, Myeshia Johnson. Trump and some of his senior White House officials have denied that was the case.

The other U.S. soldiers killed in the operation were Staff Sgt. Jeremiah Johnson, 39; Staff Sgt. Bryan C. Black, 35; and Staff Sgt. Dustin Wright, 29. Johnson was a conventional soldier trained to work with chemical, biological, radiological and nuclear weapons, while Black and Wright were Green Beret soldiers.

The U.S. military has not clarified publicly when exactly Johnson died, although the military did announce that he "died Oct. 4 in southwest Niger as a result of enemy fire."

Myeshia Johnson told ABC's "Good Morning America" on Monday that U.S. military officials said she should not view her husband's remains. Dunford, asked about that, said afterward that a casualty assistance officer may suggest that a family may not want to see their loved one's remains, but that it is the family's choice.

"I don't know what happened in the case of Mrs. Johnson, but we'll certainly find that out," Dunford said. "From a policy perspective, we would typically defer her to the family's desires, and we do that."

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