Two former Kenyan ministers planned the country's deadly post-election violence long before the 2007 vote took place, a war crimes prosecutor told the International Criminal Court Thursday.

William Ruto, once seen as a potential candidate in next years's presidential polls, and Henry Kosgey appeared at the Hague-based court Thursday in a hearing where prosecutors will try to convince the court they have enough evidence to go to trial on charges of crimes against humanity.

"Since at least December 2006, Henry Kosgey and William Ruto created a criminal plan to gain political power," ICC top prosecutor Luis Moreno-Ocampo said at opening day of the hearing, set to run until September 12.

"The crimes were planned and prepared long before the elections happened," he said.

Ruto and Kosgey both backed then opposition candidate Raila Odinga, now Kenya's prime minister, in the disputed December 27, 2007 polls, that sparked election clashes where, according to prosecutors, 1,133 people died.

"Mr Kosgey and Mr Ruto held at least eight meetings in 2007," Moreno-Ocampo said. "They provided weapons and phones and promised land to those participating in the attack. They offered money to those who killed and those who burned."

Radio executive Joshua arap Sang also faces crimes against humanity charges and was in court Thursday.

Ruto, 44, served as Kenya's agriculture and then as higher education minister. Kosgey, 64, was the east African nation's industrialisation minister.

Kenya was plunged into violence after the 2007 general elections in which Odinga accused President Mwai Kibaki of having rigged his way to re-election.

What began as political riots soon turned into ethnic killings targeting Kibaki's Kikuyu tribe.

They launched reprisal attacks in which homes were torched and people hacked to death. Prosecutors said Thursday that some 663,000 people were displaced in the country's worst violence since independence in 1963.

Ruto's group faces charges including murder, forcible transfer and persecution committed against perceived supporters of Kibaki's Party of National Unity (PNU) following poll results.