Kenyan presidential election heads to nail-biting finish NAIROBI (Reuters) - Kenya's presidential race has tightened as early pace-setter Uhuru Kenyatta's lead shrank over his main rival Prime Minister Raila Odinga, raising the prospect of a second round run-off. Deputy Prime Minister Kenyatta, 51, who is due to go on trial at the Hague for crimes against humanity linked to the violent aftermath of the last election in 2007, had led since results started trickling in after polls closed on Monday. Results from strongholds loyal to Odinga, 68, closed the gap, but with a quarter of votes yet to be counted, the contest still could go either way. By 06:00 p.m. EST on Thursday, with 7.51 million total votes tallied, Kenyatta had 3,700,967 or 49.3 percent, to Odinga's 3,366,757 or 44.81, according to a display by the electoral commission at the national tallying center. However, this tally was only for 169 constituencies out of a total of 291, meaning it could change either way. Counting has been unexpectedly slow, with a final result not seen until Friday at the earliest. An outright win by either candidate would require more than 50 percent of the vote, short of which a run-off is mandatory. Turnout was estimated at more than 70 percent of the 14.3 million eligible voters, who were undeterred by pockets of violence that killed at least 15 people. The poll is seen as a critical test for east Africa's largest economy, whose reputation as a stable democracy was damaged by the bloodshed that followed the 2007 election. Much will rest on whether the final result is accepted, and whether any challenges take place in the courts or on the streets. Despite the delays and technical glitches, international observers have broadly said the vote and count were transparent. But Odinga's camp challenged the process on Thursday when the tally still showed Kenyatta on course to win in a single round. They said counting should be stopped because it lacked integrity and that some results were being "doctored," raising tensions in what so far has been a mostly peaceful process. Election officials, who have up to seven days from Monday's vote to declare the outcome, said the count would not stop. Issack Hassan, chairman of the Independent Electoral and Boundaries Commission, said the vote tally was genuine. The European Union ambassador to Kenya, Lodewijk Briet, said the vote counting was sound and should be allowed to continue. As chairman Hassan has just said it should not be stopped midway. It should continue. If people have a problem with the integrity, the legal disputes settlement mechanism exist and should be followed," Briet told Reuters. The Kenyan shilling has swayed against the dollar, gaining on reassurances of a smooth counting process and buckling on concerns that delays in announcing a winner would prompt rivals to challenge the election outcome. Analysts said a run-off would unnerve markets by prolonging the uncertainty. Both men deny the charges and have said they plan to clear their names. The Jubilee coalition has also complained about the delays, and accused British High Commissioner Christian Turner of seeking to meddle in the vote. Turner said the accusations were "entirely false and misleading," showing how brittle both sides in the race have become in a tense race. Additional reporting by Yara Bayoumy; Writing by James Macharia; Editing by Michael Roddy