A supporter of Kenyan opposition presidential candidate Raila Odinga pauses during a march in the Mathare slum in Nairobi on August 10, 2017, following an announcement by the opposition party, two days after the election.
The foreign missions said they have worked hand in hand with the Kenyan people and with Kenya's institutions to prepare for free, fair, credible and peaceful elections.
The IEBC public website, which is publishing results as they stream in electronically from polling stations, shows Kenyatta with 8.1 million votes, ahead of Odinga with 6.7 million.
As of Thursday afternoon, election officials were waiting to receive about 170 forms from the country's 290 constituencies and about 1,000 forms from the 40,883 polling stations. The opposition's dispute over the results sets the stage for a repeat of the election-related violence that has stalked Kenya since it became a multiparty democracy in 1991.
Kenyans are still awaiting the results of Tuesday's presidential vote.
"We are supposed by now to have had results, but the delay has been caused by the fact that the opposition had complaints about the system of transmitting results", Mogambi said.
Yakub Guliye, election commissioner in charge of information technology, said the opposition had not made a formal request and it would not act on a verbal request.
Opposition supporters in Kibera have burned tires and shouted slogans, hours after clashes between police and protesters erupted in Kawangware, another poor area of the capital.
The Independent Electoral & Boundaries Commission will declare the outcome of the vote at 2 p.m.in the capital, Nairobi, spokesman Andrew Limo said in a mobile-phone text message.
"Hacking was attempted but did not succeed, that is our position", said Chebukati.
Most of this East African country nation has remained calm since the vote, but several people have been shot and killed in clashes between police and opposition supporters.
Kenyatta is already on track for a win (97 percent of stations reporting, Kenyatta: 54.32 percent; Odinga's 44.8 percent).
The alliance's "outright declaration that Odinga is the rightful victor raises the risk of further violence in opposition areas should the IEBC confirm Kenyatta's victory", Emma Gordon, an analyst at Bath, England-based Verisk Maplecroft, said in an emailed note.
Heading the Carter Center's observer team, former US Secretary of State John Kerry said the integrity of the process is still intact.
"We have one person killed and four others admitted in hospital with gunshot injuries", said Dr Ojwang Lusi, the regional health chief in western Kisumu county.
NASA had alleged on Tuesday that the electoral commission's system was hacked and that the results transmitted to the IEBC that places the incumbent in the lead were fictitious.
They had used the log-in details of top IT official Chris Msando, found murdered and tortured last month, he said.
Over 400 global election observers - including officials from the United States and the European Union - were deployed across the country to monitor voting, the tallying process and part of the post-election period.
"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", Kerry says.
"It is the paper ballots and the accounting process established by the IEBC that tell the story of this election, not the electronic transmission of those numbers", Kerry said.
The alliance, known as Nasa, sent a letter to the IEBC with its list of demands, including that the authority stop releasing unverified results, Mudavadi said.
"IEBC must not hurry the announcement until all parties are satisfied beyond doubts with results in the spirit of fairness", added Mudavadi.
The IEBC insists its electronic voting system - seen as key to avoiding fraud - had not been compromised, despite apparent attempts to do so.