Kenyan Presidential candidate Uhuru Kenyatta casts his vote on March 4, 2013. With half the votes counted, Kenyatta was leading Prime Minister Raila Odinga by 54 percent of the vote to 42 percent. (Ben Curtis/AP)

With nearly half the votes counted, Uhuru Kenyatta and his running mate, both indicted by the International Criminal Court for crimes against humanity, continued to lead by a wide margin Wednesday morning in Kenya’s presidential election.

The 51-year-old Kenyatta, the current deputy prime minister and son of this East African nation’s founding father, was leading Prime Minister Raila Odinga, 68, by 53 percent of the vote to 42 percent, according to early provisional results from polling stations.

But already there are signs that the results could be placed in doubt. Kenya’s electoral commission said more than 300,000 “spoiled ballots” were tossed away because they did not follow election guidelines. Odinga’s supporters demanded that the commission consider the rejected ballots, which could prevent Kenyatta from winning more than 50 percent of the vote, required by Kenya’s constitution to avoid a run-off scheduled for April.

Late Tuesday night, the electoral commission’s chairman announced that that the rejected ballots will be counted in the overall vote total, making it highly likely that a run-off election between Kenyatta and Odinga will take place. Adding to the concerns were delays in the tallying of votes due to breakdowns in equipment and other issues.

William Ruto, Kenyatta’s running mate, reportedly blamed western powers for pressuring the electoral commission on its decision to include the rejected ballots. He told the Standard Newspaper, a respected local daily, that the decision “is meant to deny us a first-round win.”

A heavy police and military presence remained in Nairobi and in other parts of the nation. Public demonstrations have been banned out of concern that ethnic violence could erupt, particularly in Nairobi’s slums, the wellspring of chaos in Kenya’s previous disputed elections five years ago.

The election is the most complex in Kenya’s history, with citizens voting simultaneously for presidential, provincial and local candidates, including women’s representatives and county senators. The presidential race alone had eight candidates. A change in the election rules meant that voters had to cast six ballots in separate boxes for national and local races, leading to many “spoiled votes,” according to Isaak Hassan, chairman of Kenya’s Independent Electoral and Boundaries Commission.

The commission expects to have a preliminary result by Wednesday in the presidential race. Hassan cautioned the public Tuesday that thousands of polling stations had yet to release results. And Odinga’s supporters said many of their strongholds appeared to be slower in reporting returns.

“Nobody should celebrate; nobody should complain,” said Hassan, whose comments were televised. “We therefore continue to appeal for patience from the public, the political parties, as well as the candidates.”

In Kenya’s disputed 2007 elections, Odinga declared that he was cheated out of the presidency, triggering an explosion of ethnic violence that killed more than 1,000 Kenyans and splintered the country.

If Kenyatta and his running mate, William Ruto, emerge victorious, it would mark the first time that a nation has democratically elected two candidates indicted by the International Criminal Court (ICC). They could face much of their term on trial in The Hague, where proceedings against them are scheduled to begin in April. Both men are accused of instigating the ethnic mobs that rampaged through Kenya’s countryside and slums in Nairobi, murdering and pillaging.

Unusually vocal, U.S. and Western diplomats have publicly cautioned that Kenya might face consequences if it elected a president indicted by the ICC. Britain’s high commissioner, the country’s top envoy in Kenya, even declared on a local television station that Britain would not hold talks with any of those indicted by the ICC “unless it was essential.”

The ICC case was a key factor in some Kenyans’ choice for president, even though the vast majority voted along tribal lines, as expected, according to the provisional election results.

Kenyatta “can’t run the country while he’s facing trial,” said Emmanuel Mutoko, 21, a musician.

But others said they supported Kenyatta and that they believed he was innocent of the ICC charges — or at least innocent until proven guilty.

“We are going to win,” declared Chege Kimani, 60, a retired teacher, shortly after he voted. “There will be no runoff.”

Millions of Kenyans voted Monday under heavy security, even as marauding gangs killed six police officers in the southern coastal city of Mombasa.

Despite the new bloodshed, Kenyans across Nairobi and in most parts of the country patiently waited for hours in long, snaking lines to cast ballots for presidential, parliamentary and provincial candidates.

The voting unfolded peacefully in most parts of the nation, despite problems with digital equipment and delays at some polling stations. The turnout — about 14 million Kenyans are registered to vote — is predicted to be the biggest in the country’s history.

“It’s very different from 2007,” said Ruth Namulundu, an election monitor in the Nairobi slum of Kibera, an epicenter of the violence that ignited after the December 2007 elections. “It’s more calm now. If the voting continues like this, everything will be fine.”

Still, a predawn assault on Monday that killed the six police officers in Mombasa served as a reminder of the existing tensions and how easily violence can erupt. Police officials said a gang of 200 men wielding machetes clashed with police who were deployed to keep the peace during the vote. Police said the assailants were suspected of being members of the Mombasa Republican Council, a regional separatist movement that opposes the elections.

Besides Kenyatta and Odinga, six other candidates also are vying for the presidency.

It was Odinga’s bitter loss to outgoing President Mwai Kibaki that ignited the ethnically charged attacks in 2007, mostly pitting Odinga’s Luo tribe and Kibaki’s Kikuyus. Kenyatta, also a Kikuyu, and his running mate, William Ruto, were indicted by the International Criminal Court (ICC) at The Hague, accused of instigating the mobs that perpetrated the violence. If they are elected, they could face a significant portion of their term on trial for crimes against humanity.

Long a key U.S. ally, Kenya is an important counterterrorism partner in the fight against al-Shabab, a militia linked to al-Qaeda in neighboring Somalia. Kenya is also an economic powerhouse, vital to keeping stability in the region.

On Monday, Odinga, Kenyatta and Ruto urged their followers to preserve the peace, no matter who wins.