Prominent Black Lives Matter activists and celebrities have written to Nigeria's president demanding justice over the treatment of people during protests against police brutality.

The group, which includes singer Alicia Keys and campaigner Greta Thunberg, urged President Muhammadu Buhari to free jailed protesters.

They also called for a "transparent investigation" into the alleged killing of protesters by armed forces.

"We cannot stay silent," they said.

Witnesses say they saw soldiers open fire on protesters at a toll gate in the wealthy Lagos suburb of Lekki on 20 October. It followed weeks of protests, which began against the now-disbanded, much-hated police unit, the Special Anti-Robbery Squad (Sars), but then morphed into greater calls for better governance.

"In the midst of a global pandemic, your people sought to bring peace and justice to their land, and they made Africa and its diaspora proud in doing so," the letter to President Buhari said.

"Yet their peaceful requests were met with state-sanctioned violence and suppression, as your administration meted out unwarranted force against its own unarmed citizens."

The letter was organised by #BlackLivesMatter movement co-founder Opal Tometi, and timed to coincide with International Human Rights Day.

Other signatories included actors Kerry Washington, Danny Glover and Mark Ruffalo, as well as writers Afua Hirsch, Reni Eddo-Lodge and Naomi Klein.

"As people who have supported the Black Lives Matter movement in the United States and throughout the diaspora, we cannot be silent when similar atrocities take place in African countries," the letter said.

"We demand respect for the Nigerian people, especially as they engage in their constitutional right to protest grave injustices."