Nigeria’s electoral board said Tuesday the outcome of governorship polls in six states was inconclusive, sparking opposition fury and raising the prospect of re-runs and legal action.

It said violence and other irregularities had prompted voting Saturday to be cancelled in some areas of Kano and Sokoto, in the northwest, Bauchi and Adamawa in the northwest, and the central states of Benue and Plateau.

“We have concluded elections in 22 states. We have six states inconclusive and one suspended, that is Rivers,” said Festus Okoye, from the Independent National Electoral Commission (INEC).

In areas where the poll was cancelled, the total vote exceeded the margin between the top two candidates, which prompted returning officers to declare the outcome for that state to be inconclusive, he told AFP.

“They did not satisfy the margin of lead principal as stated in our regulations and guidelines,” he said.

The development comes after election observers criticised the organisation and running of Saturday’s vote, as well as presidential and parliamentary polls on February 23.

The European Union said on Monday there were “systemic failings and electoral security problems” in both that indicated a “real need for serious reform”.

President Muhammadu Buhari’s beaten rival, Atiku Abubakar, of the Peoples Democratic Party (PDP), called the vote a “sham” and is challenging the result in court.

The PDP said it was “clearly leading the (governorship) race” in the affected states and accused INEC of collusion with Buhari’s ruling All Progressives Congress (APC).

INEC was “seeking ways to use the situation to aid the APC to alter the results and announce APC candidates as winners”, it said in a statement on Monday evening.

Sokoto governor Aminu Tambuwal said he would challenge the decision in court.

The situation comes after INEC suspended the count in the southern state of Rivers for 48 hours on Sunday after violence and the invasion of a collation centre by men in uniform.

The PDP called the suspension “a barefaced assault… akin to a coup d’etat”. The military has blamed political thugs dressed in army fatigues.

Local elections are fiercely contested in Nigeria, as powerful governors generally have more impact on ordinary people’s day-to-day lives than presidential and parliamentary votes.

Governors control huge budgets and are responsible for areas such as infrastructure, and the provision of health and education.

Nigeria is split into 36 states and the Federal Capital Territory of Abuja. Going into the election, the APC held 22 states and the PDP 13.

According to results declared by Tuesday morning, the APC was ahead by 11 states to nine.