Lagos -Sixty-six violent incidents marred Nigeria's closely-fought regional polls, with restive oil-producing Rivers state the worst affected, the election agency said Sunday.
The Independent National Electoral Commission (INEC) however praised the nationwide voting on Saturday as "relatively peaceful".
INEC also said in a statement that electronic voter identification devices -- which were used for the first time in last month's general election and caused headaches in several states -- broadly worked in the regional vote despite problems in some areas.
But the commission lamented the "significant number of violent incidents" recorded across the country.
INEC spokesman Kayode Idowu told AFP that the commission would not comment on the number of casualties that resulted from the unrest.
Also read: INEC office in Rivers set ablaze
The southern Rivers state saw 16 separate outbreaks of violence on Saturday, the statement said, with the remaining 50 incidents spread throughout the country.
Voting was extended into Sunday at nine wards in Rivers after vital election material was not delivered to a number of polling stations.
The results from Saturday's vote were cancelled in several areas where ballot papers were openly stolen, said INEC's top official in the state, Gesila Khan.
The opposition All Progressives Congress has accused President Goodluck Jonathan's Peoples Democratic Party of orchestrating a massive ballot stuffing campaign in the state.
Despite losing nationally to challenger Muhammadu Buhari in the presidential vote, Jonathan won Rivers with more than 95 percent support.
A total of 29 governorship and deputy governorship positions from Nigeria's 36 states are up for grabs as well as seats in all of the states' legislatures, with results expected to trickle in on Sunday.
For the latest on national news, politics, sport, entertainment and more follow us on Twitter and like our Facebook page.