By Katie Nguyen and Wangui Kanina

NAIROBI, May 4 (Reuters) - A leading Kenyan opposition figure and presidential hopeful accused the government on Friday of planning a campaign of "insecurity and mayhem" to intimidate voters in the run-up to this year's elections.

In a Reuters interview, Raila Odinga also criticised his former ally, President Mwai Kibaki, for failing to do more to stop land clashes that have killed at least 140 people in the western Mount Elgon area over the past six months.

These clashes and others in Kiambu and Tana River regions have fuelled fears of worsening insecurity before the anticipated December vote in a country with a history of pre-election violence.

"We have some information that there are plans to cause insecurity and mayhem in several parts of the country as a way of trying to scaring the wananchi (Kiswahili for citizens) -- particularly in areas hostile to the government -- from participating in the elections," Odinga told Reuters.

Asked who was behind the plan, he said: "The government."

Government spokesman Alfred Mutua said Odinga's allegations were "preposterous" and intended for political gain.

"We should not politicise security issues. If he has any information, he should pass it on to the police instead of making wild allegations," Mutua told Reuters.

Kenya's last elections, held in 2002, were peaceful compared with the tribal clashes that accompanied the 1992 and 1997 campaigns in which 2,000 people were killed and thousands more forced from their homes.

But riots and killings marred Kenya's last major vote, a 2005 referendum on a new constitution. Many Kenyans say the violence was the work of politicians from both sides of the government-opposition divide.

PRESIDENTIAL BID

Odinga formed the opposition Orange Democratic Movement-Kenya (ODM-K) along with Kibaki critics and other dissident ministers sacked for opposing the government-backed charter in 2005.

Odinga, he son of Kenya's late nationalist hero, Jaramogi Oginga Odinga, plans to launch his bid to be ODM-K's presidential candidate on Sunday -- the fifth party member to do so.

He was confident the fledgling party would survive the crowded race for presidential candidate and overcome rivalries between the contenders.

"I still believe very strongly that ODM will hold together. We have a common objective to dislodge the government in power," Odinga said.

"I think it's too late in the day for somebody to start a movement that will make a difference in the elections," he added.

The veteran politician, who carries the support of slum dwellers in the Nairobi and his western Luo tribe, is famous for his populist charisma.

The 62-year-old recently grabbed headlines when he rode to parliament in a flashy Hummer H2 truck, believed to be the first in Kenya.

Odinga spent eight years in prison, six in solitary confinement, on treason charges during former president Daniel arap Moi's regime.

Despite falling out with Kibaki and Moi, Odinga said he had invited both to his launch.

"I never want to live in the past. That's why I say let bygones be bygones. And I'm trying to reconcile this society, hence my statement that I will not (take) revenge in the event I'm elected president," Odinga said.

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