A European Union observer mission has faulted the lack of transparency and operational failures in the Nigerian election, according to its preliminary findings.

It said there was confidence in the independence and professionalism of the electoral body during preparations for the elections.

But public trust waned over lack of efficient planning and effective communication in the process - including on the election day, the observers said.

Nigerians cast their votes in a presidential and parliamentary general election on Saturday.

The observers noted that some poll centres opened late and polling procedures were not always followed.

They said the uploading of the results using an electronic system did not work, raising concerns as transmission of presidential election results forms was delayed.

The observer team has urged stakeholders in the election to uphold peace until the process is completed and called for any disputes arising to be addressed through legal channels.