Kenyan Deputy Premier Uhuru Kenyatta used a criminal network together with police to attack opposition supporters after Kenya's disputed 2007 polls, the world war crimes court heard on Wednesday.

Kenyatta, 49, and two other top ruling Party of National Unity (PNU) officials are facing judges at an International Criminal Court hearing to determine if they should be prosecuted for the violent aftermath of Kenya's polls which prosecutors say left more than 1,000 dead.

"Crimes were committed by the leaders of the PNU in association with the Mungiki and with the collaboration of the police," ICC prosecutor Luis Moreno-Ocampo told the hearing in The Hague, referring to Kenya's powerful underground criminal organisation.

Kenyan President Mwai Kibaki's right-hand man Francis Muthaura, 64, and ex-police chief Mohammed Hussein Ali, 55, are also facing charges for their part in the violence. The men, who each face five counts of crimes against humanity committed in the aftermath of Kenya's controversial polls, remain free.

All supporters of Kibaki's PNU, the three are suspected of devising and implementing a plan to attack rivals of then opponent and now Prime Minister Raila Odinga's Orange Democratic Movement (ODM).

"The crimes," said Moreno-Ocampo on Wednesday, "were a response against the crimes committed by the leaders of the ODM."

The prosecutor referred to a meeting on December 30 2007, following the disputed polls where he said Kenyatta proposed to use the Mungiki in reprisal attacks against ODM supporters.

"Mr Kenyatta in this meeting proposed to use the Mungiki to fight back," Moreno-Ocampo said.

Prosecutors alleged Kenyatta, a potential presidential candidate in 2012 and the son of Kenya's founding father Jomo Kenyatta, was "closely associated with the Mungiki."

The Mungiki are described as a mafia-like group similar to a sect inspired by the Mau-Mau who fought for Kenyan independence with a mystical blend of Christian doctrines with traditional African practices.

The organisation, whose strongholds are in Nairobi and in areas of the dominant ethnic group in Kenya, the Kikuyu, has gradually turned into a group engaged in racketeering widely known for beheading some of his victims .

The ICC prosecutor's office said 1,133 people died and more than 663,000 others were displaced after clashes between the rival supporters, when political riots turned to ethnic killings, sparking further reprisals.

The hearings, during which prosecutors will try to convince the court they have enough evidence to go to trial, are scheduled to run until October 5.

The three are the second group of senior Kenyans to appear before the Hague-based court after ICC prosecutor Luis Moreno-Ocampo in December 2010 asked judges to issue summonses against them for crimes against humanity.

Earlier this month ex-Kenyan ministers William Ruto and Henry Kosgey, as well as radio executive Joshua arap Sang, also appeared before the court to determine if they should stand trial for their part in the violence.

Supporters of Odinga's ODM, they are accused for their part in attacks on PNU members in the Rift Valley. They all protested their innocence and the court's decision is still awaited.

Kenya last month lost an appeal to stop the ICC from trying the six men, with the court turning down a request to have them in the dock in Nairobi.