Nigerians on Tuesday evening watched in horror as soldiers fired on a peaceful crowd of mostly youthful demonstrators singing the national anthem in the country's largest city, Lagos, with Amnesty International reporting at least 12 killed.

Some dismayed Nigerians then criticized President Muhammadu Buhari for not mentioning the killings and instead warning citizens against ``undermining national security.''

On Saturday, Nigerians living in the United Kingdom marched through London to condemn the shooting of people protesting police brutality. Demonstrations have also been in the US and South Africa.

The government has insisted that the protests, while well-intentioned, were hijacked by thugs who looted and burned vehicles and businesses in the two days after the soldiers opened fire.

Buhari has said 51 civilians were killed, along with 11 police officers and seven soldiers.

The scenes in Nigeria have struck a chord with the Black Lives Matter movement in the United States, and the shootings by soldiers sparked immediate international condemnation.

By not taking action against security forces, some Nigerians have warned, the president could inspire further abuses.

Some business owners took advantage of the relative calm to open. Others were out to inspect the damage to their premises.

The new police order came even as a 24-hour curfew loosened for the first time Saturday in Lagos, a city of some 20 million where glittering wealth and grinding poverty are in sharp contrast, inflaming grievances over inequality and corruption.

The police inspector general "enjoins law-abiding citizens not to panic but rather join forces with police...to protect their communities from the criminal elements," the statement said.

Elsewhere in Lagos, some youth took to the streets again Saturday, but this time to clean up some of the debris after the turmoil. Charred vehicles remained in some parts of the city.

"A lot of harm has happened to people's business and our heart goes out to them,'' said one volunteer, Monica Dede.

As for the way forward in Nigeria, she said, "we will still be heard, we will not be shut up, we will definitely push for what we believe in as the youths of Nigeria. We are part of the system, we are part of this governance."