Nigerians are scheduled to vote in a presidential and parliamentary election on Saturday, and the killing in Enugu came hours after the parties and presidential candidates signed a pledge to support a peaceful electoral process.
Chinwuba Ngwu, the Labour Party chairman in the Enugu South local government area, said senatorial candidate Oyibo Chukwu had been ambushed and killed as he traveled back from a campaign event.
"He was shot dead and then set ablaze in his vehicle with his driver and one of his boys," Ngwu said.
"It is a devastating development for us. We are suspecting political assassination because he is favored to win the election," he said.
A police spokesperson in Enugu State confirmed the incident and said they would issue a statement later.
Nigeria, Africa's most populous nation and biggest economy, has a long history of election-related violence.
U.S. President Joe Biden earlier called for a peaceful, transparent election, urging parties and candidates to accept the results when they are published by the Independent National Electoral Commission.
