WASHINGTON — U.S. Sen. Tim Kaine is accusing the military of hiding from Congress its true mission in a Niger ambush last October that ended in the deaths of four American Green Berets.

Following a classified briefing from senior Defense Department officials to the Senate Armed Services Committee, senators confirmed the fatal mission had been to “capture-or-kill” a target and not simply a training activity with local forces.

“That was a very explosive briefing,” said Sen. Tim Kaine, D-Va. “I have deep questions about whether the military is following the instructions and limitations laid down about the missions about these troops in Africa.”

Kaine questioned whether the legal authorization to conduct a train-and-equip missions in Niger is “really a fig leaf” and said he believes the military is hiding its true activities.

The briefing, “raises questions about why people are hiding from us what they’re doing,” Kaine said.

A military investigation into the Niger attack that killed the American service members concluded the 12-man team didn’t get required senior command approval for its risky mission to capture a high-level Islamic State militant, the Associated Press reported in March.

Initial information suggested the Army Special Forces team set out on its October mission to meet local Nigerien leaders, only to be redirected to assist a second unit hunting for Doundou Chefou, a militant suspected of involvement in the kidnapping of an American aid worker. Officials say it now appears the team went after Chefou from the onset, without outlining that intent to higher-level commanders.

As a result, commanders couldn’t accurately assess the mission’s risk, according to the officials, who spoke to AP on condition of anonymity.

North Carolina Republican Sen. Thom Tillis, whose state is home to the four Fort Bragg soldiers killed and Joint Special Operations Command, confirmed after the hearing Tuesday that there had been a failure to communicate to the chain of command the nature of the mission.

“Clearly, some things in terms of their concept of operations, they made some mistakes, and it costs our men their lives,” Tillis said, adding of military witnesses: “I think they understand it now … They readily pointed out problems and specific changes that have been made.”

Tillis said the briefing did not touch on whether anyone in the chain of command had been held accountable, but he expected to see whether there would be any personnel action in the coming days.

Witnesses at the hearing included Assistant Secretary Of Defense For Special Operations And Low-Intensity Conflict Owen West, Assistant Secretary Of Defense For International Security Affairs Robert Karem, Marine Corps Gen. Thomas Waldhauser, the chief of U.S. Africa Command, and Army Maj. Gen. Roger Cloutier, Africom’s chief of staff.

Alaska Republican Sen. Dan Sullivan, who confirmed the troops were on a “capture-or-kill” mission, questioned why highly-trained special operations forces should be fighting in Niger when the new National Defense Strategy has marked a focus on competition with Russia and China and a shift away from counter-terror operations.

“I don’t know if we need 1,000 troops in Niger,” he said. “You have this not just a teachable moment on the tactics … but on the broader strategic approach to special operations forces to the National Defense Strategy.”

“If we’re putting our highest value trained soldiers on capture or kill missions, [the targets] should be individuals who threaten the country, our country,” Sullivan said.

South Dakota Republican Sen. Mike Rounds said the troop deaths call into question why troops there must borrow assets from other agencies.

Rounds may have been referencing reports that a request by U.S. military officials were denied a request to send an armed drone near the ill-fated group of Green Berets. Since, construction on an Air Force drone base in Agadez, Niger, has made headlines.

Calling the briefing “very comprehensive,” Sen. Jeanne Shaheen, D-N.H., said, “It raises a lot of questions about future operations.”