The ambush that left four U.S. soldiers dead in Niger earlier this month was partially the result of a "massive intelligence failure," NBC News reported Friday, citing a senior congressional aide.

The unnamed aide, who NBC News said had been briefed on the deaths, said that the House and Senate Armed Services committees were looking into the U.S. military's presence in the northwest African country and whether they were receiving adequate support from the Pentagon.

The aide said there was no overhead surveillance of the mission involving the 10 U.S. soldiers on patrol, and that there was no American quick-reaction force on hand to back the soldiers up in case they encountered a dangerous situation.

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U.S. officials told NBC News that any conclusions regarding an intelligence failure are premature.

The Pentagon has opened a formal investigation into the troop's deaths, while lawmakers continue to raise questions about the mission and seek answers from the Trump administration.

The body of Sgt. La David Johnson was found 48 hours after troops realized he was missing, and roughly a mile away from the attack, CNN reported on Friday.

The U.S. military routinely investigates the death of American soldiers, with Defense Secretary James Mattis James Norman MattisBiden courts veterans amid fallout from Trump military controversies Trump says he wanted to take out Syria's Assad but Mattis opposed it Gary Cohn: 'I haven't made up my mind' on vote for president in November MORE telling reporters this week that officials were still seeking answers about the attack.

"These terrorists are conducting war on innocent people of all religions, they are conducting war on innocent people who have no way to defend themselves," Mattis said.

"In this specific case, contact was considered unlikely, but there's a reason we have U.S. Army soldiers there and not the Peace Corps, because we carry guns," he said.