"We believe the IEBC (election commission) put in place a detailed, transparent process of voting, counting, reporting and securing the vote, all of which lends significant credibility and accountability", Kerry told a press conference.
Kenyans are nervously watching results from the election between President Uhuru Kenyatta, who is ahead in the vote count as he seeks a second term, and Raila Odinga, who alleges that the electoral commission's database was hacked.
Mudavadi said the opposition had gotten the information from "confidential" sources inside the election commission.
Global observers praised the handling of the election, with the European Union saying it had seen no sign of manipulation despite opposition complaints and scattered protests.
Supporter of opposition leader Raila Odinga set up flaming tyre barricade in Kibera slum in Nairobi, Kenya, August 9, 2017.
This warning was ignored. "This attack on our democracy has affected our presidential election in all 47 counties", Mr. Odinga said. The IECB said it hoped to release final results from the presidential poll on Friday.
Kenyan opposition leader and presidential candidate Raila Odinga says hackers have fixed the election result
The opposition leader, running in his fourth presidential election, claimed that the systems of the Independent Electoral and Boundaries Commission (IEBC) were hacked using the identity of Chris Msando, the late head of IT at the IEBC.
In the city of Kisumu, police used tear gas and shot at protesters who were upset after Mr Odinga's fraud allegations, said demonstrator Sebastian Omolo.
With results from nearly all of the polling stations counted, President Uhuru Kenyatta was shown with a wide lead over Odinga in his bid for a second term. He has stood by the statement that he made on Wednesday that led to the first wave of violence that killed 4 people. The ethnic and political violence that followed killed 1,200 people and displaced 600,000.
"We affirm the conviction that the judicial process, the judicial system of Kenya, and the election laws themselves make full and adequate provision for accountability in this election".
On the ground, unrest was reported in Kisumu, an opposition stronghold on the shores of Lake Victoria.
"We have caught them".
With 97 percent of stations totalled, Kenyatta was leading with 54.32 percent of the votes versus Odinga's 44.8 percent, while none of the other six candidates managed more than 0.3 percent of the votes.
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