Poster of Nigeria's rulling party presidential candidate Umar Yaradua (l)and his running mate Goodluck Jonathan in Port Harcourt

Nigeria's ruling People's Democratic Party has taken a commanding lead in state elections that have been marred by violence and allegations of fraud.

Authorities said Sunday that at least 21 have been killed in violence related to Saturday's vote for 36 state governors.

Partial results released by Nigeria's electoral commission show that President Olusegun Obasanjo's party has won 10 states while opposition parties have carried two.

Saturday's voting was disrupted by pockets of violence and allegations of ballot-box stuffing and other irregularities.

Opposition groups have rejected the results as rigged.

Police Inspector General Sunday Ehindero called for calm Sunday and announced a ban on demonstrations about the election.

The state elections are a prelude to next Saturday's presidential vote. Obasanjo is required to step down next month after serving two four-year terms.

Some information for this report was provided by AFP, AP and Reuters.