A preliminary report probing last October's deaths of protesters in Lagos also said that there was an attempt to cover up and conceal the incident, including by police officers who picked up bullets.
Nigerian security forces have shot and "killed unarmed" demonstrators in a crackdown last year that could be considered a "massacre".
A commission probing the deaths of Nigerian protesters in Lagos last October released a preliminary report on Tuesday that directly contradicts Nigeria's army's denial that troops opened fire with live rounds.
"At the Lekki Toll Gate, officers of the Nigerian Army shot, injured and killed unarmed helpless and defenceless protesters, without provocation or justification," the commission said in one of its key findings, according to the report.
"The manner of assault and killing could in context be described as a massacre."
Amnesty International said at the time at least 10 people were shot dead by security forces.
The commission’s report noted 11 people killed, four more missing, presumed dead, and a further 21 wounded by gunshots from the Lekki site.
The commission said police officers also tried to cover up their actions by picking up bullets.
"The panel also found that the conduct of the Nigerian Army was exacerbated by its refusal to allow ambulances render medical assistance to victims," it said.
Activists involved in the protests welcomed the initial findings.
Moe Odele, a lawyer who helped coordinate the protests, wrote: "#LekkiMassacre happened".
"Shattered so many lives, tried to destroy mine. Only for what you desperately tried to hide to be made public… by you!" DJ Switch, one of the protest organisers who was at Lekki and later went into exile, said on Twitter.
Shattered so many lives, tried to destroy mine. Only for what you desperately tried to hide to be made public… by you!— Dj Switch (@dj_switchaholic) November 15, 2021
The truth needs no defense! #EndSARS
Protests over police brutality
The army has said that only blank rounds were fired to disperse a crowd at Lekki that was breaking a night-time curfew.
Lagos State Governor Babajide Sanwo-Olu has promised a proper response to the panel's recommendations, adding that its decision would be published within the next two weeks.
The #EndSARS protests initially erupted over police brutality, but grew into the largest anti-government demonstrations in the modern history of Africa's most populous nation.
The independent judicial commission had been set up by Lagos state government to investigate the crackdown at the city's Lekki tollgate, the epicentre of the #EndSARS protests.