Kenya's knife-edge election count has been halted while the country's electoral commission reviews dozens of disputed constituency results.
Kenya's opposition leader Raila Odinga has called on President Mwai Kibaki to admit defeat in national elections, or stage a full recount.
Official returns do not tally with results given to local party agents in a number of seats.
He accused Mr Kibaki of electoral fraud and described the counting process as "deeply flawed".
The delays have prompted allegations of rigging and sparked violence, with at least three deaths reported.
The count has been halted while the country's electoral commission reviews dozens of disputed results.
The BBC's Adam Mynott in Nairobi says President Mwai Kibaki may have taken a lead over his opponent Raila Odinga.
The delays prompted allegations of vote rigging and sparked violence, amid reports that three people had died.
Official figures from the Electoral Commission of Kenya still gave Mr Odinga the lead, with 3.88m votes to Mr Kibaki's 3.84m, based on results from 180 out of a total 210 constituencies.
Mr Odinga of the Orange Democratic Movement had held the lead since vote counting began, but he has since seen his advantage evaporate.
Roadblocks and bonfires
While the presidential candidates are neck-and-neck, the election has seen a clear rejection of Mr Kibaki's government, with about 20 ministers losing their seats.
There were scuffles at the counting centre in Nairobi, when election chair Samuel Kivuitu announced results that largely cancelled out much of Mr Odinga's lead.
As rival party agents clashed, paramilitary police had to rush in and restore order.
Mr Kivuitu told politicians: "Nobody can push me, not even you!" He added: "We are Kenyans, not beasts."
The BBC's Karen Allen in Nairobi says Mr Kivuitu has outlined a number of electoral irregularities that have dogged the process.
These include returning officers vanishing due to intimidation and a case in one constituency of turnout being higher than the number of registered voters.
Mr Kibaki's Party of National Unity said it would wait for the official results, and urged officials to speed up the count.
The European Union's election observer, Alexander Lambsdorff, said there was a massive question mark over the tallying of votes.
Both sides have raised allegations of vote rigging and rioting has broken out in some opposition strongholds.
There were also reports of trouble in Kisumu, Bungoma, Busia, Eldoret, Kericho and Kakamega.
Police have fired tear gas and gunshots into the air to disperse angry demonstrators who lit bonfires, set up roadblocks and even burned down homes.
Several people have died in the violence, including a man shot dead in a row at a polling station in western Nyanza province, police said.
"They want to steal votes. They are counting votes from regions favouring Kibaki and then they want to declare him the winner," said one protester, Peter Oduor.
Ethnic violence
Much of the violence was enacted along ethnic lines, with Luo supporters of Mr Odinga clashing with members of Mr Kibaki's Kikuyu tribe.
An Electoral Commission spokesman told the BBC that turnout had perhaps been more than 70%, from an electorate of 14m.
Results so far show a majority of MPs have lost their seats.
Kenyan parliamentarians gained notoriety in the past five years for arbitrarily increasing their salaries and allowances, while a majority of Kenyans continued to grapple with meagre wages and a high cost of living.
Vice-President Moody Awori was one of about 20 ministers who lost their seats.
The vote also saw three sons of retired president Daniel Arap Moi lose their seats in three different constituencies in the Rift Valley province.
Mr Moi has helped fund Mr Kibaki's campaign. If he loses, Mr Kibaki, who came to power with a landslide victory in 2002, will be Kenya's first sitting president ousted at the ballot box.
