International observers have widely applauded the electoral commission’s conduct, and note that the official results are based on paper ballots tallied and verified at polling stations, not those transmitted electronically.

There has been no evidence so far that votes have been tampered with at polling stations or that the results contradict reports from party agents present during the counting of ballots, said John Kerry, the former United States secretary of state and an election observer for the Carter Center.

“So obviously there is a moment of reckoning coming up pretty soon,” he said in a telephone interview. “And the reckoning will be based on a paper trail.”

The electoral commission has already received nearly all documents detailing the results from each polling station, Mr. Kerry said. “The process is very meticulous and, plus, all the parties have copies of the documents,” he said. “So there is a huge trail of documentation. All of that will ultimately give confidence to people that they can trust in the outcome of the vote.”

Another top Western observer, speaking on the condition of anonymity because observers do not want to be seen as interfering, cast doubt on Mr. Odinga’s assertions. She said she had seen no evidence of vote-rigging.

The new claims by the opposition came a day after Mr. Odinga said that election commission servers had been hacked to award Mr. Kenyatta a 10-point lead. Mr. Odinga described the 2017 election a “fraud.”

The hackers, he told reporters earlier this week, had used the credentials of an election official who was killed days before the vote to gain access to the servers and then doctor the results. “They loaded an algorithm which is a formula to create a percentage gap of 11 percent between our numbers,” he said.