Sporadic gunshots were heard in Lagos on Friday as security forces patrolled Nigeria's biggest city after days of unrest following the shooting of protesters that sparked condemnation at home and abroad.

President Muhammadu Buhari warned demonstrators in a televised address on Thursday not to "undermine national security" as he called for an end to widespread protests gripping Africa's most populous country.

The 78-year-old leader was speaking for the first time since the shooting in Lagos on Tuesday, although he did not directly address the incident.

He appealed to the youth to "resist the temptation of being used by some subversive elements to cause chaos".

"For you to do otherwise will amount to undermining national security and the law and order situation. Under no circumstances will this be tolerated," Buhari said.

- 'Please stay indoors' -

Nigeria, where many live in extreme poverty and where the median age is 18, is a tinderbox of economic and social grievances.

"Police officers are currently patrolling major parts of the city to ensure the safety of residents. Please stay indoors," Lagos State Police Command said on Friday.

Protests against police abuse erupted on October 8 after a video of an officer allegedly killing a civilian went viral.

Despite the disbanding of the police unit accused of brutality, the federal Special Anti-Robbery Squad (SARS), protests spread and violence escalated.

Anger spread further after pictures and videos on social media showed security forces shooting on a peaceful crowd of around 1,000 protesters on Tuesday.

Amnesty International said 12 people were killed in the incident, with a total of 56 people dead in the unrest across the country.

- 'Rushing to judgement' -

US Secretary of State Mike Pompeo called for an immediate investigation into violence by security forces, which has also triggered condemnation by the United Nations, the African Union, the European Union and others.

Nigeria's president shrugged off the international concern.

"We thank you and urge you all to seek to know all the facts available before taking a position or rushing to judgement and making hasty pronouncements," Buhari said.

The spreading of "deliberate falsehood and misinformation, in particular through social media" was, he said, "a ploy to mislead the unwary within and outside Nigeria into unfair judgement and disruptive behaviour."

After the president's speech, a key protest group told its followers to "stay home" but many made it clear that the movement would continue.

"The past two weeks have been tough for many Nigerians, most specifically the last two days," the Feminist Coalition said in a statement.

"We hereby encourage all young Nigerians to stay safe, stay home, and observe the mandated curfew in your state."

Others in the youth-led movement insist that the demonstrations will continue.

"Everybody, get your PVC (electoral card) ready," tweeted Afrobeats star Davido.

"This was just practice. We go again! Now we must deploy our unity and experienc