Nigeria's biggest city Lagos and several states were under curfews on Wednesday as unrest rooted in anti-police protests broke out again following a day of violence, including the shooting of civilians by security forces.
Fires burned across Lagos and residents reported hearing gunfire despite President Muhammadu Buhari's appeal for "understanding and calm".
Armed police tried to enforce a round-the-clock curfew in the commercial capital, setting up checkpoints. But groups of young men blocked a number of major roads with overturned traffic signs, tree branches and rocks. Smoke billowed from buildings that were ablaze.
Video verified by Reuters showed armed police in the Yaba area of Lagos kicking a man as he lay on the ground. One officer fired into his back and dragged his limp body down the street.
Images taken afterwards showed crowds gathering, thick black smoke from burning tyres and more police officers with guns drawn and pointed.
Rights group Amnesty International said the Nigerian army and police killed at least 12 peaceful protesters at two locations in Lagos - Lekki and Alausa - on Tuesday.
At least 56 people have died across Nigeria since nationwide protests began on Oct. 8, with about 38 killed on Tuesday alone, Amnesty said.
A Lagos police spokesman said via WhatsApp that he was "not aware of any such allegation" regarding the man who was kicked and shot, and said that there were no killings in Alausa, which he said is "a very peaceful place."
Thousands of Nigerians, many driven closer to poverty by the economic fallout from the coronavirus pandemic, have joined the protests that initially focused on a police unit, the Special Anti-Robbery Squad (SARS).
The unit - which rights groups have long accused of extortion, harassment, torture and murder - was disbanded on Oct. 11 but the protests have persisted with calls for more law enforcement reforms.
Governor Babajide Sanwo-Olu imposed the curfew on Lagos on Tuesday.
But a shooting on Tuesday night at a toll gate in the Lagos district of Lekki, where people had gathered in defiance of the curfew, appeared to mark the worst violence since the protests began and drew international concern over the situation in Africa's most populous country, a major oil producer.
"There is little doubt that this was a case of excessive use of force, resulting in unlawful killings with live ammunition, by Nigerian armed forces," United Nations High Commissioner for Human Rights Michelle Bachelet said on Wednesday.
The African Union Commission's chairman said he "strongly condemns the violence".
And the Economic Community of West African States (ECOWAS) urged Nigerian security forces to exercise restraint in handling protests and to act professionally.
Sanwo-Olu said 30 people were hurt in the shooting. Four witnesses said soldiers had fired bullets and at least two people had been shot at the toll gate. Three witnesses said the gate's lights were turned off before the shooting began. One said he saw soldiers remove bodies.
The Nigerian Army said no soldiers were at the scene.
Inyene Akpan, 26, a photographer, said more than 20 soldiers arrived and opened fire as they approached the protesters.
Witness Akinbosola Ogunsanya said the lights suddenly went out around 6:45 p.m. (1745 GMT) and men came beforehand to take down CCTV cameras. Minutes later, soldiers in uniform walked towards the crowd, shooting as they walked, he said. He saw about 10 people being shot and soldiers removing bodies, he said.
Another witness, Chika Dibia, said soldiers hemmed in people as they shot at them.
Henry Kufre, a television producer, said the atmosphere had been peaceful and people were singing the national anthem before the site was plunged into darkness and the shooting began.
Buhari said on Wednesday he was committed to providing justice for victims of brutality, and that the police reforms demanded by the demonstrators were gathering pace. He did not refer to the shooting at the toll gate.
Vice President Yemi Osinbajo late on Wednesday on Twitter expressed sympathy for victims of the Lekki shootings and others who have died in recent days. "We can and will get justice for all of them," he tweeted.