Police have said at least 10 people were killed — five in the town of Onitsha, Anambra state, and five in Asaba, in neighbouring Delta state — in violence linked to the commemoration on May 30.
The Indigenous People of Biafra (IPOB) movement, which has revived calls for an independent homeland for the Igbo people in southeast Nigeria, claimed at least 35 were killed.
Amnesty said it was unclear exactly how many people lost their lives, as soldiers — who the army says acted in self-defence — took away the dead and injured.
But it stated that based on visits to hospitals and mortuaries at least 17 were killed and nearly 50 injured in Onitsha alone.
“The real number is likely to be higher,” it added in a statement, saying some of the dead and injured seen by researchers had been shot in the back, indicating they were fleeing at the time.
“Opening fire on peaceful IPOB supporters and bystanders, who clearly posed no threat to anyone is an outrageous use of unnecessary and excessive force and resulted in multiple deaths and injuries,” said Amnesty’s Nigeria director, MK Ibrahim.
One person was shot dead as they slept, he added.