Police raided an office of Zimbabwe's prime minister on Sunday, arresting four officials a day after a key vote in the African nation.

The officials are accused of impersonating police, Zimbabwe police spokeswoman Charity Charamba told reporters.

The raid came a day after a national referendum to approve a new constitution that would impose presidential term limits for the first time in Zimbabwe. The results of the voting are not yet known. And it came just a few months before Prime Minister Morgan Tsvangirai is expected to run against President Robert Mugabe in presidential elections.

Tsvangirai's office said in a statement that the officials were arrested after a raid on his communications office. Police also arrested Beatrice Mtetwa, a prominent human rights lawyer, accusing her of "defeating the course of justice," Charamba said.