A propaganda video released by Islamic State appears to show an ambush in Niger that killed four American soldiers last year.

In the video, three American soldiers have few resources to fight off dozens of militants armed with machine guns and grenades. Part of the nine-minute recording appears to be taken from the helmet camera of one of the fallen soldiers. That segment shows two other soldiers shooting and running beside an SUV while taking fire near the village of Tongo Tongo.

The video ends with the soldier wearing the camera falling and being surrounded by militants who shoot at him.

The Pentagon on Monday said it was aware of the video. "The release of these materials demonstrates the depravity of the enemy we are fighting," it said.

The ambush on Oct. 4, 2017, prompted an investigation by the Pentagon into whether the soldiers were appropriately trained and armed for a mission in the west African nation. The results are expected to be released this month.

A team of 12 soldiers was on a mission with a team of Nigerien troops.

Army Sergeant La David Johnson and Staff Sergeants Bryan Black, Jeremiah Johnson and Dustin Wright were killed in the ambush.