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(CNN) —  

Virginia Democratic Sen. Tim Kaine said Wednesday that “people will be held accountable” for unauthorized portions of a mission involving Americans soldiers in Niger, four of whom were later killed in an ambush.

Kaine, who sits on the Senate Armed Services Committee and the Foreign Relations Committee, told CNN’s “New Day” that during a briefing Tuesday, he and other senators learned that the troops initially attempted to embark on a search for a high value target, a mission they were not authorized, trained or equipped to conduct. They later reverted to an advisory capacity with the Nigerien forces they were working with.

“I believe that the troops who were sadly killed in Niger in October of 2017 were engaged in a mission that they were not authorized by law to participate in and that they were not trained to participate in. And that is a significant reason that they tragically lost their lives,” he added.

Kaine refrained from further details about the mission because of classified nature of the briefing.

The Virginia senator told CNN that other senators left the briefing “somewhat shocked.”

“After the hearing yesterday we had huddled. We are going to figure out a way that the story will be told and that people will be held accountable,” he added.

The team that was attacked in Niger was given several different tasks before it was ambushed, but its primary mission was to advise and assist a unit of 30 Nigerien soldiers officials familiar with the investigation have told CNN.

Several officials said that two junior officers had initially sought to carry out a high value target mission that they did not have authorization to conduct but the team was redirected to a lower risk mission more in line with their authorized mission.

Eventually the team was tasked with visiting a known to be abandoned encampment to collect intelligence on the ISIS suspect. They did not encounter any enemy forces at the site, which had been under surveillance for hours, and left the location.

On their way back to base, they stopped in a separate village in order to enable the Nigerien troops to replenish supplies. While there, US troops met with local leaders as a courtesy.

The US officials said it was “quite probable” that someone in the village tipped off the ISIS-affiliated terrorists that US forces were in the village, setting up the ambush.

CNN’s Ryan Browne, Arwa Damon, and Brent Swails contributed to this report.