Nigeria's President Muhammadu Buhari has appealed for "understanding and calm" after protests against police brutality in Lagos turned bloody on Tuesday and Wednesday, with eyewitnesses and Amnesty International telling CNN that multiple demonstrators had been shot dead at Lekki toll gate and another site by Army soldiers, who then took the bodies away.

The statement, signed by the special adviser to the president, Femi Adesina, did not mention the attack at Lekki toll gate or any of the deaths reported by Amnesty. Nigerians have called for the President to address the nation directly about the attacks that rocked the country on Tuesday and Wednesday.

The president is the commander-in-chief, which means the deployment of troops should have been approved by him. Former Nigerian president Olusegun Obasanjo appealed to Buhari to "restrain the military and other security agencies" in a statement on Wednesday.

Franklin Alex spoke to CNN while hiding in his home in Ebute Metta, about 9km (10 miles) from the Lekki toll gate. He said the police had been on his street earlier on Wednesday morning, and that three people had been killed. He added that officers at four police stations nearby were firing at protesters.

"The police are shooting at people that are not armed, though some of them have bottles and stones, but the police are using very sophisticated weapons on them," he said. "They are moving from street to street, I could count about 17 of them, all armed, all shooting."

Videos posted on social media and local television coverage showed a number of buildings on fire, including the Lagos Theater and at least one bank branch. Some police stations were also attacked, and video also showed the High Court of Lagos on fire.

Human rights group Amnesty International said that after an on-the-ground investigation it had found that twelve people were killed during protests in two locations in Lagos on Tuesday.

It said that "evidence gathered from eyewitnesses, video footage and hospital reports" confirmed that over a period of about two hours "the Nigerian military opened fire on thousands of people who were peacefully calling for good governance and an end to police brutality."

The army has dismissed reports that protesters were shot dead as "fake news." The Nigerian Army and police did not return requests for comment.

Eyewitnesses told CNN shots rang out during a peaceful protest at the Lekki toll gate in Lagos as activists chanted the national anthem and asked for police brutality to end.

Daily protests have been held across the country for close to two weeks, over widespread claims of kidnapping, harassment, and extortion by a police unit known as the Special Anti-Robbery Squad (SARS).

Akinbosola Ogunsanya, a talk show host on Afrosurge Radio, said the shooting began shortly after the lights at the tollgate were switched off. "Members of the Nigerian army pulled up on us and they started firing," he said. "I just survived, barely."

CNN couldn't independently corroborate the witness accounts.

Multiple witnesses told CNN they saw the army take the bodies away.

Christopher Yakubu, 27, who told CNN he fell and injured his leg while trying to escape the gunfire, showed CNN a video of his injury. "I heard rapid shots. I couldn't count them. I counted 5 bodies," he said. "Later I saw that the Nigerian Army took the bodies in their own van. We couldn't take videos," he said.

Another protester also said he witnessed the bloodshed.

"They killed more than 7 people and got away with their bodies to cover up evidences," said Deji Jokodola.

On Tuesday, Lagos state governor Babajide Sanwo-Olu imposed a 24-hour curfew and deployed anti-riot police to the city.

In a televised statement on Wednesday morning, Gov. Sanwo-Olu insisted nobody had been killed at Lekki toll gate: "Whilst we pray for the swift recovery of the injured, we are comforted that we have not recorded any fatality."

Later in the day, he tweeted that one person had died at Reddington Hospital due to "blunt force trauma" to the head. He said it was an isolated case and said he was investigating whether the dead person was a protester. CNN reached out to the Governor's office, but did not receive a reply.

Eyewitness reports

The Governor's comments directly contradict statements from several eyewitnesses who said they had seen multiple casualties at the protest.

Speaking to CNN from the scene of the shooting, Temple Onanugbo said he saw "multiple bodies laying on the ground," when he arrived to help those injured. He said he heard what he believed were bullets being fired from his home nearby and that the sound lasted "for about 15 to 30 minutes."

"I was on Instagram Live when the shooting started," Henry Pundit, a filmmaker, told CNN. "They were coming to us with multiple gun shots. We went on the ground and held our flag. We were crying, some were running."

Amnesty International Nigeria tweeted that it had received "credible but disturbing evidence" of "excessive use of force occasioning deaths of protesters."

Gov. Sanwo-Olu asked for all forms of protest to end immediately and ordered an investigation into the incident. "Yesterday's events were no doubt some of the darkest gradients of our history as a state and as a people," he said.

Earlier on Tuesday, the governor imposed a 24-hour curfew on Lagos -- which has an estimated population of more than 20 million people -- including the closure of all its schools.

The lockdown means that only essential service providers and first responders have permission to be on the streets.

SARS was disbanded on October 11 and a new police unit to replace it will be trained by the International Committee of the Red Cross (ICRC), Reuters reported Sunday.

Protesters are demanding further protections against the police, including independent oversight and psychological evaluation of officers.

International condemnation

On Wednesday, US Democratic presidential candidate Joe Biden urged President Buhari and the Nigerian military to halt "the violent crackdown on protesters in Nigeria which has already resulted in several deaths."

UK Foreign Secretary Dominic Raab said he was "deeply concerned by the recent violence and continued clashes in Nigeria," and "alarmed by widespread reports of civilian deaths."

"We call for an end to violence," Raab added. "The Nigerian government must urgently investigate reports of brutality at the hands of the security forces and hold those responsible to account."

Former US Secretary of State Hillary Clinton urged Buhari to do something to end the violence. "I'm calling on @mbuhari and the @hqnigerianarmy to stop killing young #EndSARS protesters. #StopNigeriaGovernment," she said in a tweet.

Manchester United's Nigerian soccer player Odion Ighalo said he was "ashamed of this government" in an Instagram post. "I'm calling on the UK government, calling all those leaders in the world to please see what is going on in Nigeria and help us."

Death and severe injuries amid the protests have been reported since the weekend.

Videos on social media show dozens of cars belonging to protesters burning, which Amnesty International Nigeria confirmed on Twitter.

"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 human rights group tweeted.

Other videos show a mass breakout of hundreds of prisoners from the Benin Correctional Center in Edo state in southern Nigeria. It is uncertain who is to blame for the breakout, with protesters claiming it was staged by police. The Nigeria police force said in a tweet that protesters carted away arms and ammunition from the armory before freeing suspects in custody and setting the facilities alight.

Edo state governor Godwin Obaseki imposed a curfew on Monday, tweeting about "disturbing incidents of vandalism and attacks on private individuals and institutions by hoodlums in the guise of #EndSARS protesters."

Riot police have been deployed across the country. According to a tweet from the Nigerian police force on Tuesday evening, the Inspector-General of Nigeria's Police has ordered the immediate nationwide deployment of anti-riot police officers "to protect lives and property of all Nigerians and secure critical national infrastructure across the country."