Kenyan deputy president William Ruto urged thousands of his followers to slaughter their neighbours, provided them with money and weapons and denounced their victims as "snakes" and "witches" who must be eliminated, prosecutors say.

The allegations emerged as Mr. Ruto walked into a courtroom in The Hague on Tuesday, becoming the first sitting government leader to stand trial at the International Criminal Court for crimes against humanity.

Kenya's president, Uhuru Kenyatta, is due to face similar charges at the same court in November. The charges relate to a brutal wave of violence after Kenya's 2007 election, when more than 1,000 people were killed and about 600,000 were forced from their homes. The ICC stepped into the case after Kenya refused to set up domestic tribunals to prosecute those who orchestrated the bloodshed.

Story continues below advertisement

Despite the charges against them, Mr. Kenyatta and Mr. Ruto were elected as Kenya's leaders in March, capitalizing on a growing public mood that the court is discriminating against Africans. They portrayed themselves as victims of a global conspiracy.

Many witnesses against the Kenyan leaders have died or disappeared or withdrawn their testimony, and prosecutors have complained of systematic attempts to bribe and intimidate witnesses. Kenya's parliament voted last week to withdraw from the ICC. But the prosecutors are vowing to proceed with the cases, insisting that they still have strong evidence.

"This was a carefully planned and executed plan of violence," ICC chief prosecutor Fatou Bensouda told the court on Tuesday. "Ruto's ultimate goal was to seize political power for himself and his party in the event he could not do so via the ballot box. … It is difficult to imagine the suffering or terror experienced by the men, women and children who were burnt alive, hacked to death or chased from their homes."

Mr. Ruto pleaded not guilty to all of the charges Tuesday. Reporters in the courtroom said he seemed relaxed as he laughed and smiled with his lawyers. Dozens of Kenyan MPs packed the courtroom to show their support for him.

So far, Mr. Ruto and Mr. Kenyatta have said they will co-operate with the court, but Mr. Kenyatta has warned that the co-operation could end if both of the leaders are summoned to the court at the same time.

A radio host, Joshua arap Sang, is also accused of crimes against humanity for allegedly broadcasting appeals to Mr. Ruto's followers to begin their attacks. His trial also began on Tuesday.

The violence after the December 2007 election was horrific. Youths rampaged through the Rift Valley and other regions of Kenya, burning houses and murdering people with machetes, spears and bows and arrows.

Story continues below advertisement

In a 64-page court document summarizing the evidence against Mr. Ruto, prosecutors said he personally planned and organized the attacks by his ethnic Kalenjin followers, providing weapons to them, supplying maps of targeted houses, and offering financial rewards for those who attacked and killed ethnic Kikuyus in the Rift Valley.

"As election day approached, Ruto hosted thousands of youths at his house in Sugoi on Dec. 14, 2007," the court document says.

"Ruto affirmed the plan of waging war to expel and kill the targeted communities and destroy their properties. Ruto paid and armed thousands of warriors – according to their military background – in preparation for the attacks, and designated a pecuniary reward for killing a Kikuyu or destroying a house, seeking promises from the crowd to kill and displace the targets and destroy their properties."

Human rights groups, including many in Africa, have welcomed the trial. "For decades those who have turned Kenya's elections into bloodbaths have gotten away with murder," said a statement by Daniel Bekele, Africa director at Human Rights Watch.

"This ICC trial tackles an impunity crisis in the country. … Every time the ICC process inches forward, the country's political establishment scrambles furiously to block the way."