NAIROBI, Kenya—The chief of Kenya’s electoral commission said he wasn’t able to deliver a credible election next week amid meddling from candidates and threats of violence, casting further doubt on the vote just hours after a top electoral official said she had resigned and said she feared for her life.

The country has been plunged into political turmoil since the Supreme Court annulled the August election and ordered an Oct. 26 redo, saying there were major problems with the original count.

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