* Polls close, initial results start trickling in
* Outgoing president, candidates call for peaceful vote
* Nine security officers among dead in Mombasa area
* More than 1,200 were killed after a disputed 2007 poll
* Mombasa killings blamed on separatists, not political rivals
At least 15 people were killed in attacks by machete-wielding gangs on Monday as Kenyans voted in large numbers in the first presidential election since a disputed 2007 poll unleashed weeks of tribal bloodshed.
Initial provisional results began trickling in moments after polls closed, showing Deputy Prime Minister Uhuru Kenyatta slightly ahead of Prime Minister Raila Odinga, with ballots in from 10 percent of the polling stations, but it was still too early to predict the outcome.
Voting in the tight contest passed off largely peacefully across most of the East African nation, although many of its 14.3 million voters were caught in long queues.
The electoral authority said early indications showed turnout above 70 percent.
Officials and candidates have made appeals to avoid a repeat of the tribal rampages that erupted five years ago when disputes over the result fuelled clashes between tribal loyalists of rival candidates.
More than 1,200 people were killed, shattering Kenya's reputation as one of Africa's most stable democracies and bringing its economy, sub Saharan Africa's fourth-largest, to a standstill.
Just hours before voting began, at least nine security officers in the restive coastal region were hacked to death in two attacks, and six attackers were killed, regional police chief Aggrey Adoli said.
Senior police officers blamed the attacks on a separatist movement, suggesting different motives to those that caused the post-2007 vote ethnic killings that could limit their impact. SUSPECTED GRENADE A suspected grenade attack on Monday at an election centre in the eastern town of Garissa near the Somali border caused panic among voters but no injuries, a government official said.
Two civilians were shot dead in Garissa on Sunday, while a bomb blast in the Mandera area near the border wounded four. As in 2007, the race has come down to a high-stakes duel between two candidates, this time between Kenyatta and Odinga, the loser in 2007 to outgoing President Mwai Kibaki. Both contenders will depend heavily on votes from their tribes.
The United States and Western donors are worried about the stability of a nation that is an ally in the fight against militant Islam in the region.
They are also concerned about how to respond to a victory by Kenyatta, who faces charges by the International Criminal Court of orchestrating violence five years ago. "If elected, we will be able to discharge our duties," said Kenyatta's running mate, William Ruto who also faces charges of crimes against humanity.
"We shall cooperate with the court with a final intention of clearing our names." Some polling stations were still open because their opening was delayed and some still had long queues. The election commission has seven days to announce the official outcome. Polls suggest there could be a run-off, provisionally set for April. The European Union observer mission said turnout was high even at the coast where the attacks took place.
One of the attacks on Monday took place on the outskirts of Mombasa and another in Kilifi about 50 km (80 miles) to the north. Police blamed a separatist movement, the Mombasa Republican Council (MRC), which wanted the national vote scrapped and a referendum on secession instead. At the Kilifi site, a piece of paper lay on the ground with the words: "MRC.
Coast is not Kenya. We don't want elections. We want our own country." But the group's spokesman denied responsibility and said it only sought change by peaceful means. Kenya's neighbours have been watching nervously, after their economies suffered five years ago when violence shut down regional trade routes. Adding to tension, the al Shabaab Islamist militant group battling Kenyan peacekeeping troops in Somalia urged Muslims to boycott the vote in Kenya and wage jihad against its military.
Voters were undeterred. In the early hours, some blew whistles and trumpet-like "vuvuzelas" to wake up voters, and queues formed hours before polls opened at 6 a.m. "Our future is uncertain but we long for peace and victory is on our side this time round," said Odinga supporter Eunice Auma, 32, in Kisumu, where violence flared after 2007.
"However, should our candidate fail to clinch victory, I'm afraid violence will erupt," she said. Although Odinga and Kenyatta are well ahead of the other six contenders, polls suggest they will struggle to secure an outright win, which could make for a tense run-off. A narrow first-round victory for either could spark legal challenges. To try to prevent a repeat of the contested outcome that sparked the violence after the December 2007 vote, a new, broadly respected election commission is using more technology to prevent fraud, speed up counting and increase transparency.
Alongside the presidential race, there are elections for senators, county governors, members of parliament, women representatives in county assemblies and civic leaders.