National Super Alliance flag bearer Raila Odinga has said he is disappointed with international election observers over their view that Kenya polls were credible.
In an interview with CNN on Thursday evening, Mr Odinga said the observers concentrated on voting and tallying but not the transmission of the results.
"I think that the observers have not helped Kenyans resolve this dispute, they have confounded it by giving basically an approval to a fairly flawed process... and therefore I am very disappointed with John Kerry and the other observers," he said.
Mr Odinga said Nasa does not want violence and appealed to its supporters to remain calm.
"We know the consequences of 20017 and we do not want to see a repeat of that anymore," he said.
On violence that was witnessed in some parts on Wednesday and Thursday, the opposition leader said he does not control anyone adding that people want justice.
CNN had earlier interviewed Mr Kerry, the head of the Carter Centre observer mission who said all nine international observers agreed that the process of carrying out the elections was "quite positive".
"The tallying is ongoing but we believe that the elections commission in Kenya has put in place a process that will allow each and every vote integrity to be proven and to be protected.
"... ..There is a way to go back, if anything was changed, if anything was fiddled with, to absolutely ascertain what happened in the polling station," he said.
Mr Kerry said it is important for the tallying process to be completed for the Independent Electoral and Boundaries Commission (IEBC) to show Kenyans how they conducted an elections that is accountable.
He said anyone with concerns afterwards should follow the rule of law and go through the court process.
"I believe that there is great legitimacy in the basic process, the question that now has to be tested is did everybody follow it, and has it in fact, somebody attempted to alter it at any stage" he said.
On Thursday, international observers said voting had been largely peaceful and thanked Kenyans for turning up at polling stations to choose their leaders.
They also called for lawful settlement of disputes arising from the elections.
Mr Kerry has said his team was satisfied with measures put in place by IEBC to conduct credible elections and added that minor variances from established process would not affect the overall integrity and process of the polls.
In July, Nasa had welcomed the appointment of Mr Kerry as an election observer.
Mr Odinga had said the coming of the former the US Secretary of State to Kenya signified the importance of the elections, which must be held in an acceptable standard.
"Secretary Kerry has a long and distinguished history of supporting democratisation in Kenya," Mr Salim Lone, Mr Odinga's adviser, had said.