A comprehensive probe into last years deadly assault of US and local forces in Niger uncovered a series of avoidable blunders leading up to the attack, the Pentagon said Thursday.

Four American soldiers and four Nigerien partners were killed in the October 4 ambush, when scores of jihadists overran their convoy in southwestern Niger, near the Mali border.

While the Pentagon said all four US soldiers fought bravely and "died with honor," investigators found they had not been properly trained ahead of the mission and pointed to problems with how it was approved in the first place.

The US soldiers, who belonged to a special operations team, had deployed to the western African nation in the autumn to conduct counter-terrorism assistance and training with the Nigerien military.

But at the time of their deployment, only half of the US team had conducted any collective training together, according to an eight-page summary of findings of the investigation, which itself remains classified.

Their mission on October 3 was to "find/fix and, if possible, capture" a key member of a group calling itself the Islamic State in the Greater Sahara, the summary states.

The summary does not name him but he is widely reported to have been the group's leader, Adnan Abu Walid Sahrawi.

The US team commander, however, had "inaccurately characterized" the nature of the mission in order to get it approved at a low level instead of requesting permission from battalion-level commanders based in Chad.

The language used for the mission had been cut and paste from previous operations and "a lack of attention to detail in quality control and quality assurance," together with inadequate approvals "all contributed to a general lack of situational awareness and command oversight at every echelon," the report summary states.

And prior to setting out on the operation, the US team failed to conduct pre-mission rehearsals or battle drills with their Nigerien counterparts, the report found.

French 'show of force'

Pentagon officials also published a detailed, 10-minute reconstruction of the ambush itself, which started as the US-Nigerien eight-vehicle convoy headed out the remote village of Tongo Tongo, having stopped there for water.

The troops were not even wearing body armor when the assault first started, and had to stop their convoy to don it.

Enemy fire was initially light, but quickly intensified as jihadists surged through a wooded area alongside the convoy.

The video describes how the convoy was forced to split up and how it was outflanked by over 100 enemy fighters.

Officials praised the actions of the French air force, which flew Mirage jets in a low-altitude "show of force" over the jihadists.

Because the French could not tell where the US troops were on the ground, they did not engage the enemy, but the overflights caused them to retreat for cover, "likely saving the lives of the surviving members of the" US team, the summary states.

Enemy fire was initially light when jihadists attacked US and Nigerien forces in October 2017, but quickly intensified as militants surged through a wooded area alongside the convoy

Sergeant La David Johnson was among the four Americans killed, and the video shows he became separated from his comrades. His body was not found until 48 hours after the attack.

Johnson's death was politicized when a US congresswoman accused President Donald Trump of being insensitive during a phone call with Johnson's widow, an account she and her mother also supported while the president denied it.

Defense Secretary Jim Mattis has issued a series of recommendations in light of the report, including better pre-deployment training.