Kenya's presidential poll was "flawed" and "fell short of international standards", EU election monitors have said in an interim report on the poll.
EU monitors questioned the final results in the poll
Chief European Union monitor Alexander Graf Lambsdorff said the tallying process "lacked credibility".
Four Kenyan election commissioners also expressed unease at the result, but the government denied any irregularities.
Police and soldiers have been deployed to tackle mounting violence in the wake of President Mwai Kibaki's re-election.
At least 120 people died in the aftermath of the result on Sunday night, according to the Red Cross, though the numbers are expected to rise following further violence on Monday.
Mr Kibaki's challenger, Raila Odinga, said that if fresh killings were taken into account, the total would likely be about 250 or "slightly more".
Some of the violence took an ethnic dimension with the majority Kikuyus supporting Mr Kibaki and the Luo community seen as backing Mr Odinga.
UK Prime Minister Gordon Brown has again urged Kenya's political leaders to talk, and said: "The violence must be brought to an end."
Mwai Kibaki (pictured): 4,584,721 votes
Raila Odinga: 4,352,993
Kalonzo Musyoka: 879,903
EU observers said the country's election fell short of international standards.
"They were marred by a lack of transparency in the processing and tallying of presidential results, which raises concerns about the accuracy of the final results," the EU team said in a statement.
According to the EU, in at least two constituencies - Molo and Kieni - the results that were announced did not reflect the number of votes cast.
EU observers say they heard the voting figures being announced in Molo itself, but when the same results were announced again in Nairobi, the number of votes for Mr Kibaki was significantly higher - by 25,000.
Four of the 22 Kenyan election commissioners have expressed doubts about the veracity of the figures giving President Kibaki victory by 200,000 votes.
One of the four, Jack Tumwa, told the BBC he felt uncomfortable as the results were read out.
"After the announcement, when an independent observer from the EU group came and said the figures given for Molo were at variance with what we had announced, that really struck me hard," he told the BBC.
"That's why we felt if that is true - and I'm also saying if that is true - then perhaps it was spread all over. But this is yet to be ascertained."
But Finance Minister Amos Kimunya denied his party, the ruling PNU, or the government had been involved in rigging the poll.
He said that if the electoral commissioners had doubts, they should have raised these doubts much earlier instead.
He denied there was a crisis and said a lot of the violence on the streets of Kenyan towns and cities was caused by thugs and criminals.
Mr Lambsdorff said an independent inquiry was needed to resolve the dispute over the election and called on the Electoral Commission of Kenya to co-operate fully.
The observers say an audit of all the voting returns is vital, and called for results from every polling station to be published in newspapers and on the internet.
Both sides in the election are claiming that rigging took place at polling stations and constituency offices, and both claim to have evidence to this effect.
Mr Kibaki was declared the winner on Sunday after a controversial three-day counting process.
His challenger, Mr Odinga, said he was robbed of victory by alleged fraud.
EU monitors have joined growing calls for an independent inquiry into the election results.