Niger's ruling party candidate Mohamed Bazoum has solidified his lead in a presidential election runoff meant to usher in the first democratic transition of power in the West African nation, election commission data showed on Tuesday.

With about 97% of the ballots counted, Bazoum led his challenger, former president Mahamane Ousmane, with 55.5% of the vote, according to provisional results published by the electoral commission.

The data showed complete returns from four regions with three outstanding, and 259 out of 266 constituencies reporting.