The European Union Election Observation Mission (EU EOM) says it witnessed intimidation of voters and violence during the supplementary elections.
The rerun held in Kano, Bauchi and Benue, Plateau and Sokoto states.
In a statement, the EU EOM said police and party leaders failed to prevent attacks on electoral officials by youth gangs armed with clubs and machetes.
It said due to harassment, its observers were unable to continue monitoring polling units in Dala and Nasarawa local government areas of Kano, adding that “this compromised scrutiny of both polling and collation of results in the affected areas.”
It noted that the Independent National Electoral Commission (INEC) did not comment on electoral disturbances “throughout the day, despite its overall responsibility for the election and security arrangements”.
“On 23 March, extensive electoral security problems were observed particularly in parts of Kano where polling became inaccessible to EU observers in some areas,” the mission said.
“The environment was intimidating and not conducive to voters’ free participation in the election. Party leadership locally and centrally did not appear to take any steps to rein in supporters and prevent evident violence, intimidation or other misconduct.
“In Nasarawa local government area in Kano, EU observers witnessed organised intimidation of voters. Groups of youth with clubs and machetes patrolled the streets and the people with party agents tags harassed voters.
“During collation in Kano, EU observers saw that several INEC polling staff had been attacked. Large groups of men with weapons were not contained by the police.”
The EU said party agents interfered more in the supplementary elections than on the previous two election days.
It said: “Isolated violent incidents also disrupted voting and counting in other states. In Bauchi, EU witnessed around 50 people with clubs disrupting counting in one polling unit. In Benue, election materials were burnt and a collation officer carrying election result sheets was shot in the leg.
“EU observers in all five states also saw party agents trying to influence voters, assisting voters or voting on their behalf. EU observers also saw vote-buying in Sokoto by both the leading parties, and indications of vote buying in Kano.
“Of the 40 polling units that EU teams could fully observe, agents were present in all and in five cases were seen interfering in the work of polling officials, in Benue, Plateau and Sokoto.”
The EU EOM, however, said INEC improved logistical arrangements in most polling units, saying procedures were mostly followed with smart card readers used to accredit voters in all polling units observed.
It added that Marie Arena, the chief observer, will return in June to present the mission’s final report, which will include recommendations for future electoral processes.