The prosecutor at the International Criminal Court (ICC) has named six high-profile Kenyans he accuses of being behind the violence that followed the disputed 2007 elections.
Deputy PM and Finance Minister Uhuru Kenyatta, one of those named, immediately protested his innocence.
Some 1,200 people died and more than 500,000 fled homes in the violence.
In the peace deal that followed it was agreed perpetrators would face justice in Kenya or at the ICC in The Hague.
Kenyan MPs have so far blocked moves to set up a local tribunal.
On Monday, President Mwai Kibaki announced the government would launch its own investigation - a move his critics have denounced as an attempt to prevent suspects being sent to The Hague.
But US President Barack Obama, whose own father was Kenyan, called on the country to cooperate with the ICC.
"The path ahead is not easy, but I believe that the Kenyan people have the courage and resolve to reject those who would drag the country back into the past and rob Kenyans of the singular opportunity that is before them to realise the country's vast potential," he said.
The violence broke out three years ago after Mr Kibaki's supporters were accused of trying to rig the presidential election.
It ended when Mr Kibaki and his rival Raila Odinga agreed to share power, with Mr Odinga becoming prime minister. BBC News
