Global activists and celebrities on Thursday hit out at the Nigerian government over a violent crackdown on peaceful protesters demonstrating against police brutality two months ago.

In an open letter addressed to Nigerian President Muhammadu Buhari and made public in Lagos to coincide with International Human Rights Day, 60 activists condemned the government for "unwarranted force against its own unarmed citizens."

Writing under the auspices of Diaspora Rising, which calls itself an advocacy body formed to strengthen "bonds among members of the global Black family", the activists called for the release of jailed protesters as well as the prosecution of security operatives responsible for shooting civilians in Lagos.

They also urged the government to lift a ban on public demonstrations.

Among the signatories were US activist Opal Tometi, actors Danny Glover and Kerry Washington, Swedish teenage eco-warrior Greta Thunberg, singer Alicia Keys, civil rights campaigner Angela Davis, US congresswoman Ilhan Omar, Nigerian-American rapper Jidenna and Bernice King, the daughter of Martin Luther King Jr.

Tometi, a co-founder of the Black Lives Matter movement in the US and founder of Diaspora Rising, described Nigeria's response to the protests as "very shameful".

"Instead of showing up alongside (the people), the government went to suppress them, went to squelch the protest, and stamp it out," she said.

Amnesty International has said security forces shot and killed at least 10 people during a protest at Lekki Toll gate, the epicentre of the demonstrations, in Lagos on October 20.

But the military has denied shooting live rounds, insisting that soldiers only fired blanks at the crowds that had gathered in defiance of a curfew.

However the Nigerian authorities have said more than 100 people, including 43 security operatives, were killed nationwide following days of street protests.