NASA, according to prior reports, claimed that the IEBC systems were hacked and an algorithm introduced into the system to manipulate results in favour of Uhuru Kenyatta.
Celebrations broke out in pockets of Kenya on Thursday after the opposition said its candidate Raila Odinga should be declared victor of the presidential vote, a claim an election commission official said was "ridiculous".
Eight candidates were in the running for president, but the election is a two-horse race between Kenyatta and the Odinga.
On Thursday it demanded Odinga be declared president on these grounds.
"The streets do not", said former U.S. Secretary of State John Kerry, an election observer for The Carter Center, an worldwide democracy promotion group led by former President Jimmy Carter.
"The Kenyan people have never disappointed. every time an election has been stolen, the Kenyan people have stood up to make sure changes are made to make Kenya a better place".
Odinga described the preliminary results as "fake" and said hackers gained access to the election computer system by using the identity of the commission's technology manager who was murdered in late July.
"The process is still underway". I am very disappointed with John Kerry and the other observers.
The results would be validated and that a final decision would be announced "soon thereafter", he added.
Despite its multi-million dollar electronic voting system, the crucial evidence on voting comes from the paper forms signed at each of the country's 41,000 polling stations.
More than 1,000 people were killed in months of bloody clashes following that vote.
Odinga's opposition party, the National Super Alliance, has repeatedly called for calm as the final results are compiled.
"We continue to urge everyone to be calm, to be resilient and to be peaceful", she said. "We know the consequences of what happened in 2008 and we don't want to see a repeat of that anymore", Odinga told CNN on Thursday.
However he repeated his assertion that "I don't control anybody". What is happening is that people just want to see justice.
Kenya is the leading economy in East Africa, and any instability would be likely to ripple through the region.
Angry protests broke out in Nairobi and the western city of Kisumu, with at least one man killed by police.
In 2007, tallying was halted and the incumbent president declared the victor, triggering an outcry from Odinga's camp and waves of ethnic violence that led to International Criminal Court charges against Kenyatta and his now-deputy William Ruto.
On Thursday, Nairobi appeared to be somewhat quieter than usual, possibly because of school holidays and some concern from residents about potential violence.
Global observers have given the thumbs-up to the vote and U.S. Ambassador Robert Godec issued a statement on behalf of the diplomatic community calling for any complaints to be channelled through the courts, not street protests.
Added Marietje Schaake, the Dutch head of the European Union mission observing the vote, "Elections should never be an issue of life or death".
"We demand that the IEBC [Independent Electoral and Boundaries Commission] chairperson announce the presidential election results forthwith and declare the right honorable Raila Amolo Odinga and his excellency Stephen Kalonzo Musyoka as the duly elected president and deputy president of the republic of Kenya, respectively", said Mudavadi.
IEBC confirmed that there was an attempt to hack their systems but the person (s) was not successful.
Chebukati, who has promised to investigate any allegations of fraud, acknowledged that there had been a hacking attack, but said it had failed.
Odinga, 72, is a veteran opposition politician seen as having taken his last shot at the presidency after four unsuccessful runs.
A senior official in the election commission rejected the opposition's claim.
"We have uncovered the fraud". "The IEBC must be fully accountable".