It is not clear why the release of the video – via an IS outlet on messaging app Telegram – was delayed until now.
The video consists mainly of raw footage, including images apparently filmed using a helmet camera belonging to one of the soldiers.
The video seems to suggest that the attack was carried out by IS militants.
The deaths became a major political row in the US when the widow of one of the soldiers, Army Sgt La David Johnson, said President Donald Trump had made her cry during a condolence phone call by suggesting her husband “knew what he signed up for”.
The president later called a US congresswoman’s account of the phone call “totally fabricated”.
What happens in the video?
The propaganda film begins with still images showing an alleged pledge of allegiance to IS leader Abu Bakr al-Baghdadi by members of the Sahel-based group Jamaat Nusrat al-Islam wal-Muslimin (JNIM).
JNIM was formed from a number of West African jihadist groups in March 2017, and originally had pledged allegiance to al-Qaeda.
This alleged switch to IS was reported last month by a number of analysts, but it had not been promoted by IS outlets on social media.
The graphic video shows several armed militants walking and running in a desert area, apparently heading for the ambush, reports BBC Monitoring.
The soldiers are seen driving away in a white vehicle, with coloured smoke grenades providing cover.
After a cut in the video, the US soldiers are seen around another vehicle, with one soldier driving and the other two walking beside while seemingly firing at their attackers.
Then, one of the soldiers drops to the ground. The man wearing the helmet camera tries to raise the fallen man.
The soldier driving the vehicle jumps out and helps drag the soldier to cover, before he and the camera-wearer run into the scrub.
While running, the soldier wearing the camera falls to the ground. The footage ends with the camera unmoving, and militants surrounding the soldier, firing at point-blank range.
I had a very respectful conversation with the widow of Sgt. La David Johnson, and spoke his name from beginning, without hesitation!
— Donald J. Trump (@realDonaldTrump) October 23, 2017Loading...
What was the controversy over the deaths?
The deaths in Niger sparked controversy after President Donald Trump’s phone call to the widow of Sgt La David Johnson.
Democratic congresswoman Frederica Wilson, who knew the soldier in question, heard the call while en route to meet his body with his family, and said the president did not seem to know his name.
President Trump denied forgetting Sgt Johnson’s name in the call, saying he spoke it “without hesitation”. He said it had been a “very nice conversation”.
Sgt Johnson’s body was initially located two days after the ambush, while the bodies of the other three soldiers were discovered on the same day they were attacked, on 4 October 2017.
Why is the US in Niger?
The US has about 800 troops in Niger, which they say are there to help train local forces and support counter-terrorism efforts.
But questions have emerged about why the US troops were not more heavily armed for the failed mission.
“We should have gotten this information a long time ago,” Texas Congressman Marc Veasey told CBS News on Sunday.
“Why they were asked to continue to go onto this mission I think is something that we all need to find out.”
The Pentagon is due to release the results of their investigation into the ambush as soon as this week, CBS reports.
This was the first time US troops were killed in combat in Niger.