Ikenga Tochukwu, police spokesperson for Anambra, said three officers were killed after gunmen used improvised explosive devices and opened fire at a police station in Idemili local government area.
Gunmen had on Saturday and Sunday used petrol bombs and automatic guns to attack two police stations in Idemili and Oyi local government area, killing four officers, Tochukwu added.
He said suspected members of separatist group Indigenous People of Biafra (IPOB) were behind the attacks.
IPOB, which Buhari's government has branded a terrorist group, denied responsibility.
The southeast is home to the Igbo homeland ethnic group. An attempt to secede as the Republic of Biafra in 1967 triggered a three-year civil war that killed more than 1 million people.
In the southeast, violence by armed gangs and suspected separatist groups has killed dozens of people this year while electoral commission offices, police stations and government buildings have also been attacked.
Widespread insecurity is among the top concerns for Nigerians as they head to the polls to elect new members of parliament and a successor to President Muhammadu Buhari.