Nigeria's Lagos state government asked the army to intervene to restore order amidst anti-police brutality protests, but soldiers did not shoot civilians, the military said.

Nigeria has been on edge following one of its biggest social upheavals in 20 years. Demonstrations across the country turned violent on October 20 when witnesses in Lagos said the military opened fire on peaceful protesters shortly after local authorities imposed a 24-hour curfew, drawing international condemnation.

The Lagos government asked the army to deploy due to "violence which led to several police stations being burnt, policemen killed, suspects in police custody released and weapons carted away," the military said in a statement published late on Tuesday said.

"The Nigerian army in the discharge of its constitutional responsibilities did not shoot at any civilian as there are glaring and convincing evidence to attest to this fact," the statement said, without providing details of the evidence.

The army, which has said it was not at the site of the shooting at the Lekki Toll Gate, and the Lagos state governor's office did not respond to calls and messages seeking comment. The military statement did not say how they intervened to curb unrest beyond denying that its men shot civilians.

Police and soldiers killed at least 12 people in two Lagos neighbourhoods on October 20, according to witnesses and rights group Amnesty International. Police have also denied involvement.

Witnesses at Lekki described armed men in army fatigues arriving at the site of the peaceful protests around 7 pm, where demonstrators knelt to wave flags and sing the national anthem, before the men raised their guns and shot into the crowd.