Kenya's army has launched a huge military operation targeting a militia which has killed some 500 people in a land dispute over the past 18 months.
Political and land rivalries have reinforced each other this year
The army is using heavy artillery, hundreds of troops and helicopter gunships, in the Mount Elgon forests near the border with Uganda.
They are targeting the Sabaot Land Defence Forces (SLDF) which was blamed for the killing of 12 people last week. The militia has also been accused of links to recent political violence.
Kenyan MPs are expected to meet on Tuesday to start discussing the power-sharing deal designed to end the violence following December's disputed election.
A Mount Elgon Red Cross official said 30,000 people had fled their homes, though the Red Cross in Nairobi said they had no tally for the number of people displaced.
The operation began under cover of darkness as hundreds of Kenyan troops were driven in trucks to prepare for an offensive against the militia.
Journalists have been told not to go into the area.
But a Reuters reporter who visited Cheptais in the foothills of Mount Elgon said five army helicopters had struck a forested area.
Government spokesman Alfred Mutua said police were chasing "criminals operating from mountain hideouts".
"We're using military helicopters to get the police out there because it's high altitude," he said.
The SLDF has been carrying out an increasing number of attacks on villages, killing people, stealing cattle and destroying homes.
They claim to be fighting for land which they say belongs to the Sabaot clan of the Kalenjin community.
Correspondents say the instability in Mount Elgon is not directly related to the violence that erupted in Kenya after December's disputed presidential election.
But long-standing land disputes between different ethnic groups have overlapped with political divisions in some areas.