Nigerian politicians deny people have been killed during the protests, while Amnesty International says at least 12 have died.

At least 12 people were killed when government forces fired upon protesters during anti-police brutality demonstrations in Nigeria, Amnesty International has claimed.

Shots were fired at protesters by the Lekki toll plaza in Lagos on Tuesday night, causing injuries and an unknown number of deaths.

Human rights group Amnesty said an investigation has uncovered evidence of 12 deaths and hundreds of injuries, and accused the police and military of using excessive force.

The protests began two weeks ago after a video circulated showing a man being beaten, apparently by police officers from the Special Anti-Robbery Squad, known as SARS.

As the "End SARS" movement has spread across Nigeria over the past fortnight, at least 56 people have died - 38 of them on Tuesday alone, Amnesty claims.

Witnesses to the scenes in Lekki on Tuesday said more than 20 officers started firing at demonstrators.

Lagos governor Babajide Sanwo-Olu confirmed more than 20 injuries, but said no one had been killed.

UK Foreign Secretary Dominic Raab said he was "alarmed" by reports civilians had been killed during the protests, which have attracted attention and support worldwide.

Mr Raab said: "I am deeply concerned by the recent violence and continued clashes in Nigeria, and am alarmed by widespread reports of civilian deaths.

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

Celebrities and politicians around the world have spoken up in support of the demonstrators.

Beyonce made a statement on the Twitter feed of her charitable foundation BeyGood, saying: "I am heartbroken to see the senseless brutality taking place in Nigeria. There has to be an end to SARS.

"To our Nigerian sisters and brothers, we stand with you."

Among those who have previously expressed their support are Star Wars actor John Boyega, and musicians including Kanye West, Rihanna and Chance the Rapper.

Manchester United star Odion Ighalo called his country's government "a shame to the world", while British Nigerian boxer Anthony Joshua tweeted: "I pray God opens the gates for the heroes of Nigeria."

Protesters ignored a 24-hour government curfew and President Muhammadu Buhari's appeal for calm to continue demonstrating on Wednesday.

There were reports of gunfire across Nigeria's largest city of 14 million - including on the highway to the airport, at a major bus station, and outside the offices of a television station.

Nobel Prize winner Wole Soyinka told Sky News the atmosphere in the city was "very, very dark, very ominous".

He said he had seen lots of evidence and testimony from witnesses who said the government was responsible for the shootings.

Demonstrations and gunfire were also reported in several other Nigerian cities, including the capital Abuja.

Supporters gathered at the Nigerian High Commission in London for a march in solidarity with those in Lagos.

One man told Sky News: "The army killed people, they have killed innocent protestors and it's unacceptable."

Before the shootings in Lekki, a Nigerian police statement warned that security forces would now "exercise the full powers of the law to prevent any further attempt on lives and property of citizens".

Speaking in a televised address, Mr Sanwo-Olu said he has ordered an investigation into the actions of the military.