NAIROBI, Kenya -- Former U.S. Secretary of State John Kerry says Kenya's ability to secure its voting system "appears to be very, very strong" as violence over Tuesday's voting in the country's presidential election erupted across the country.

Kerry is leading a mission of election observers who have monitored the vote and its aftermath.

He spoke as Kenya's election commission defended its electronic voting system from opposition candidate Raila Odinga's allegations that the system was hacked. Odinga says votes were manipulated in favor of President Uhuru Kenyatta, who holds a strong lead with 96 percent of polling stations counted.

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Kerry says Kenya's leaders need to step up in the coming days and give people confidence amid fears of post-election violence.

Kenyan police opened fire Wednesday to disperse rioters in several areas after Odinga said hackers used the identity of a murdered official to infiltrate the database of the election commission and alter the results. At least three people were killed in the clashes.

Supporter of opposition leader Raila Odinga set up flaming tyre barricade in Kibera slum in Nairobi, Kenya, August 9, 2017. Goran Tomasevic

The election commission defended the voting system as secure, saying there were "no interferences before, during and after" Tuesday's election.

Election officials were verifying the final tallies Wednesday night. It was unclear how long it would take, though by law election officials have up to a week from the election to announce the results.

Odinga, a former prime minister, blamed Kenyatta's Jubilee Party for the alleged hacking. "The fraud Jubilee has perpetuated on Kenyans surpasses any level of voter theft in our country's history. This time we caught them," he tweeted.

The fraud Jubilee has perpetuated on Kenyans surpasses any level of voter theft in our country's history. This time we caught them. — Raila Odinga (@RailaOdinga) August 9, 2017

Odinga claimed Wednesday that hackers used the identity of Christopher Msando, an election official in charge of managing information technology systems. On July 31, officials announced that Msando had been tortured and killed, alarming Kenyans who feared a recurrence of political violence fueled by ethnic divisions.

Odinga posted online what he said were computer logs proving his allegation. A Tuesday morning entry in the purported computer logs that Odinga posted on Facebook reads: "Login failed for user 'msando'. Reason: The password of the account must be changed."

Rafael Tuju, a top official in Kenyatta's party, said the opposition's claims were unfounded, and Kenya's election commission said it would investigate.