Authorities blame attacks on either the outlawed IPOB movement, which is campaigning for a separate state for the ethnic Igbo people, or its armed wing, known as ESN.
Five deaths in the last month have sparked fears of "serial killings" targeting suspected sex workers and protests by women activists in the city of Port Harcourt.
Members of the banned Islamic Movement of Nigeria attending Ashura processions were killed when police opened fire on Tuesday, according to the group's statement, a claim police refuse to comment on.
President Cyril Ramaphosa says two of the victims were foreigners who were killed during a wave of attacks on foreign-owned stores followed by apparent reprisal attacks in Nigeria.
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