* Deputy president pleads not guilty in court
* Ruto on trial for post-election violence
* Trial sets stage for that of president in November
* Proceedings will test stability in Kenya and region
Kenya's Deputy President William Ruto pleaded innocent to crimes against humanity charges at the International Criminal Court on Tuesday, while back home Kenyans hoped the case would not reignite political violence they have struggled to overcome.
As the parties took their places in the courtroom before the judges arrived, Ruto appeared relaxed, laughing and smiling with his lawyers. Joshua arap Sang, his co-accused, gave a reporter the thumbs-up sign.
Ruto and Sang are charged with co-orchestrating a post-election bloodbath five years ago, working with co-conspirators to murder, deport and persecute supporters of rival political parties in Kenya's Rift Valley region.
"The crimes of which Mr Ruto and Mr Sang are charged were not just random and spontaneous acts of brutality," said Fatou Bensouda, the ICC's prosecutor, describing the charges in court.
"This was a carefully planned and executed plan of violence... Ruto's ultimate goal was to seize political power for himself and his party in the event he could not do so via the ballot box."
It is the first time such a senior official has appeared in court to face international justice while still serving in office. Kenya's President Uhuru Kenyatta, Ruto's former rival and now his political ally, will also face trial on similar charges of crimes against humanity, beginning in November.
The cases have split public opinion, and witness testimonies of the violence in 2007-08 that killed more than a thousand people could stir tension.
The cases are also a major test for prosecutors at the decade-old Hague-based ICC, who have had a low success rate and face accusations of focusing on African countries, while avoiding war crimes in other global hotspots.
Rival members of Kenyatta's Kikuyu and Ruto's Kalenjin tribes, wielding machetes, knives, and bows and arrows, went on the rampage after a disputed 2007 election, butchering more than 1,200 people and driving hundreds of thousands from their homes.
This year, Kenyatta and Ruto buried their differences and joined forces for another election, which was comparatively peaceful. Their joint Jubilee Alliance ticket was elected in March after a campaign in which their supporters criticised the ICC for meddling in Kenya's affairs.
They say their new alliance makes violence unlikely. Their supporters say the court cases risk undoing years of painstaking reconciliation, although they insist the alliance will survive.
"LET JUSTICE TAKE ITS COURSE"
In the epicentre of the violence on Ruto's political turf in the lush Rift Valley town of Eldoret, some 300 km north-west of the capital Nairobi, Patrick Muchiri said he watched the trial with several others crowded around a television at a restaurant.
"We would have wished that the cases don't take place since we have already reconciled, especially with our Kalenjin neighbours," said Muchiri, 53, a Kikuyu farmer who was evicted from his home near Eldoret by Kalenjin youth.
"But since the matter is before the ICC, let justice take its course. However, our concern is that this might create for us a big problem should they find Ruto liable. It would revive old wounds," said Muchiri, who lives at a tented camp near the town housing hundreds of displaced victims of the clashes.
In Naivasha, just north of Nairobi, where the worst revenge attacks by suspected members of a Kikuyu militia took place, Josiah Otieno, 34, a tailor, said justice would finally be done.
"After years of waiting and suffering, we now believe that justice will be done, and those responsible for our problems punished," said Otieno, who said he was assaulted by militia who set his belongings ablaze.
Kenyan public backing for the ICC has eroded. An Ipsos-Synovate poll in July showed only 39 percent still wanted the trials to proceed. It had been 55 percent in April 2012.
The charges complicate relations between Kenya and Western leaders, who see Nairobi as central to the fight against militant Islam in East Africa.
The court's public gallery was packed with dozens of Kenyan lawmakers who had travelled to The Hague in a show of solidarity with their deputy president.
"There will be an immediate response in local politics once these trials start," said John Githongo, a former government anti-corruption official turned whistleblower. "Last time the politicians managed to turn it around for alliance building and it worked extremely well. However, invariably, once the evidence starts coming out, it will bring tension."
The horrors of the election violence shattered Kenya's reputation as one of Africa's most stable countries and dealt the economy a heavy blow from which it is only now recovering.
Anger over the charges culminated last week in a vote in parliament calling for Kenya to withdraw from the international court's jurisdiction. Kenyatta threatened to suspend cooperation with the ICC if he and his deputy were summoned simultaneously, leaving no head of state in residence.
Judges said the cases would alternate at one-month intervals. Even if Kenya does quit the court, trials already under way will continue.
Bensouda, the court's prosecutor, has rejected claims of meddling, saying that the cases before the court related purely to the violence five years ago and those accused of it.
"Contrary to what has now become a rallying call for those who do not wish to see justice for victims of post-election violence, our cases have never been against the people of Kenya or against any tribe in Kenya," she said on Monday.
Both sides have been accused of intimidating witnesses, allegations they deny. Karim Khan, Ruto's lawyer, said such accusations were designed to distract attention from a fundamentally weak prosecution case.
"This case will fall apart in the end. But it will fall apart because of lack of evidence because of the deficient investigations conducted, and not for any other reason."