Gunfire was heard in Lagos on Wednesday as protesters returned to the streets the day after Amnesty International said there was “credible but disturbing evidence” of people being shot dead by police.
Many of the shootings occurred on Tuesday night in the Nigerian city's wealthy Lekki neighbourhood, with witnesses and local media reporting security forces had opened fire on demonstrators who had breached a 24-hour curfew.
People across Nigeria have been protesting for a fortnight against the Special Anti-Robbery Squad (SARS), a police unit that human rights groups have blamed for abuses including violence and torture against civilians.
The government has since disbanded the unit, but the protests have continued.
Jerry Fisayo Bambi, a journalist from Euronews's partner network Africanews, said multiple witnesses from the scene had told him soldiers had fired directly into the crowd of protesters in Lagos on Tuesday night.
At least 12 people are said to have been killed and 28 others injured, he said.
On Wednesday morning, gunshots were heard in central Lagos and shops across the city's business district were closed.
Babajide Sanwo-Olu, the state governor of Lagos, said it had been "the toughest night of our lives".
He added on Twitter that "forces beyond our direct control have moved to make dark notes in our history" — a possible implication that the federal government or Nigeria's armed forces gave the decision to open fire.
At least 30 people have been treated in local hospitals, Sanwo-Olu said.
"Amnesty International has received credible but disturbing evidence of excessive use of force occasioning deaths of protesters at Lekki toll gate in Lagos," the NGO tweeted on Tuesday night.
"While we continue to investigate the killings, Amnesty International wishes to remind the authorities that under international law, security forces may only resort to the use of lethal force when strictly unavoidable to protect against imminent threat of death or serious injury."
The protest movement, known as #endSARS, has attracted international attention, with Nigerian football stars based abroad and former US Secretary of State Hillary Clinton among those calling on the authorities to end their crackdown.
There have also been cases of looting and arson across the country in recent days.
A 24-hour indefinite curfew has been declared in cities including Lagos, but there was no immediate official confirmation of a fatal shooting in Lekki.
A short statement on Tuesday night from Gbenga Omotoso, the Lagos state commissioner for information, said only that “there have been reports of shooting at the Lekki Toll Plaza following the 24-hour curfew imposed on Lagos."
“The state government has ordered an investigation into the incident,” it added.
But the daily newspaper Punch called it "Black Tuesday" and said as many as 49 people had been killed across Nigeria. That figure has not been independently verified.