Luis Moreno-Ocampo, the International Criminal Court prosecutor, has told judges at a pretrial hearing in The Hague that three prominent Kenyans carefully plotted a campaign of murder, deportation and persecution in the country's Rift Valley region to gain political power.
The allegation was made on Thursday, the opening day of a hearing in the court's case against William Ruto and Henry Kiprono Kosgey, both legislators, and Joshua Arap Sang, a radio broadcaster, who are accused of crimes against humanity during deadly violence that erupted after Kenya's 2007 presidential elections.
Kenya's government has repeatedly argued that the case, and another linked indictment of three other Kenyan suspects, should be handled by Kenyan courts.
However, ICC appeals judges rejected that argument this week.
Moreno-Ocampo justified his decision to prosecute the case by telling judges, the "massive crimes ... are not just a Kenyan problem.
"These are some of the most serious crimes of concern to the international community as a whole and for that reason the ICC intervened".
Prosecutors and defence attorneys will spend days presenting a summary of their evidence to judges who will then decide whether the case should proceed to trial.
A decision is expected later this year.
The three suspects insist they are innocent and have challenged the court's jurisdiction.
Ruto's lawyer, David Hooper, accused Moreno-Ocampo of a "slanted and wrong interpretation of events" and said the prosecutor had failed to investigate evidence that could clear the suspects or mitigate their guilt.
Hooper said that evidence against Ruto is based on "a flawed investigation and over-reliance on a handful of anonymous witnesses".
Sang's lawyer, Joseph Kigan-Katwa, echoed Hooper's concerns, saying Moreno-Ocampo "ran away from the opportunity to know the truth".
Moreno-Ocampo is obligated by the court's founding statute to investigate both incriminating evidence and evidence that could clear a defendant.
But the prosecutor said his evidence would show Ruto and Kosgey plotted well before the December 2007 presidential elections to drive supporters of their political opponents out of the Rift Valley province with a carefully co-ordinated campaign of killings and persecution.
They used Sang to broadcast propaganda, Moreno-Ocampo alleged.
The three were supporters of Raila Odinga, the opposition candidate, and targeted backers of Mwai Kabaki, who was elected president in the vote that Odinga supporters said was rigged.
Reported death toll
Documents circulated on Thursday by prosecutors put the reported death toll of post-election violence throughout Kenya at 1,133 and said 3,561 people were injured.
A total of 663,921 people were listed as "internally displaced".
Post-election clashes occurred between tribes that supported Kibaki, a Kikuyu, and those that supported Odinga, a Luo.
Fighting stopped after Kofi Annan, the former UN chief, mediated an agreement that made Odinga prime minister.
Three other prominent Kenyans, supporters of Kibaki, face a similar hearing later this month for their alleged roles in the violence.
Sureta Chana, a lawyer representing 327 victims of the violence, said her clients' "lives, families, hopes and aspirations ... have been turned upside down" by the violence.
Many are afraid to return home because of a "continuing climate of menace" in the region.