NAIROBI: Kenyans awaited presidential results with growing frustration Wednesday at controversial delays and mountains of spoiled ballots, five years after violence sparked by a disputed tallying process.

With counting continuing into the second day since polls closed, partial results put Uhuru Kenyatta -- who faces an international trial for crimes against humanity over violence after the last elections -- in the lead.

Kenyatta, the deputy prime minister, has maintained a steady lead in partial results over rival Prime Minister Raila Odinga, but political parties on both sides have raised concerns at delays in the tallying process.

Odinga says he was robbed of victory in 2007 when disputed results triggered bloody ethnic violence in which more than 1,100 people were killed and 600,000 were forced to flee their homes.

While millions of Kenyans turned out peacefully on Monday for the elections, how they react to the final results will be key to stability in the regional powerhouse. Leaders and election officials have urged people to remain calm.

Stalled electronic voter systems meant that by midday Wednesday just over 40 percent of the almost 32,000 polling stations had sent results, making up five million valid votes counted from the 14.3 million registered voters.

Kenyatta had won just over 2.82 million or 53 percent of valid votes cast against Odinga with 2.23 million or 42 percent, a gap that could still be overturned.

More than five percent of votes cast were rejected, and those were not initially included in total tolls.

To win outright and avoid a second round run off, a candidate must win "more than half of all the votes cast", according to the constitution, as well as winning at least 25 percent of votes in more than half of all counties.

If these spoiled ballots were included, it would greatly add to the numbers needed for a candidate to break the 50 percent threshold for a first round win, raising the prospect of another round due within a month after the vote.

Kenya's Daily Nation in its Wednesday editorial warned that despite largely peaceful holding of polls there was a potential "rocky road" ahead.

"Election-related violence last time occurred not during the peaceful voting and counting, but in protest after the announcement of suspect results following lengthy unexplained delays," it noted.

Despite appeals by leaders for patience, in the western town of Kisumu, an Odinga stronghold and flashpoint in 2007-8 violence, concern was growing.

"It's taking a long time, let's hope that they are not doing something fishy," said airport worker Jack Mwai.

There have already been multiple complaints at the widespread failure of electronic biometric voting registration (BVR) kits introduced by the Independent Electoral and Boundaries Commission (IEBC) to frustrate potential rigging.

The failure meant stations used paper records and manual registration, and many returning officers were due to travel by road Wednesday to deliver results by hand.

Sitting in the near empty hall at Kisumu county tallying centre, returning officer Dolly Akili was waiting for results for one final constituency.

"Then I will get my security, they will take me to the airport to fly to Nairobi," she said, adding that she hoped to travel by nightfall Wednesday.

Kenyatta's Jubilee Coalition late Tuesday called on the IEBC to "urgently remedy the technical issues" affecting the vote count, but expressed "surprise" at suggestions by Odinga's party to include spoiled ballots in the vote count.

Kenyatta and running mate William Ruto -- who also faces trial later this year at the International Criminal Court (ICC) for crimes against humanity -- said there was "no precedent" for including invalid votes.

Rejected ballots total more than those so far won by the third candidate in the race, deputy prime minister Musalia Mudavadi, who has two percent of votes so far.

Kenya has been calm in recent days apart from isolated incidents of violence, including clashes on the coast between police and attackers that killed 12.

Bombs also exploded Monday in the northeastern town of Mandera close to the border with war-torn Somalia, as well in Nairobi's largely ethnic Somali district late on Tuesday. The attacks wounded at least two people.

The results of the 2007 poll, pitting President Mwai Kibaki against Odinga, sparked a wave of protests, notably over the lack of transparency in the way the votes were counted.

Odinga and his rival Kenyatta -- the son of independent Kenya's founding president as well as one of Africa's richest and most powerful men -- have publicly vowed there will be no repeat of the 2007-08 bloodshed.

But the trials later this year at The Hague-based ICC for Kenyatta and Ruto have raised the stakes: should they win the vote, the president and vice-president could be absent for years.