The trial of Kenya’s Deputy President William Ruto has opened at the International Criminal Court (ICC) in The Hague, Netherlands.
Mr Ruto and President Uhuru Kenyatta are accused of crimes against humanity by orchestrating violence after elections in 2007 – which they deny.
Mr Ruto becomes the first serving official to appear at the ICC.
The two trials are seen as a crucial test of the ICC’s ability to prosecute political leaders.
This is a politically controversial trial with a complex legal history, says the BBC’s Anna Holligan in The Hague.
Mr Kenyatta and Mr Ruto were on opposite sides during the 2007 election and are accused of orchestrating attacks on members of each other’s ethnic groups.
They formed an alliance for elections in March, saying they were an example of reconciliation.
Analysts say the ICC prosecutions bolstered their campaign as they portrayed it as foreign interference in Kenya’s domestic affairs.
Mr Ruto and radio executive Joshua arap Sang are accused of murder, deportation and persecution, which they both deny.
Some 1,200 people were killed and 600,000 forced from their homes in weeks of violence after the disputed December 2007 election.
The UN-brokered peace deal that brought an end to the brutal killings included an agreement that those responsible for the violence must be held to account.
A commission was set up to investigate the violence and it recommended that if efforts to establish special tribunals in Kenya failed, the matter should be sent to The Hague.
Kenya repeatedly failed to set up such tribunals and so the ICC indicted those it said bore the greatest responsibility for the violence.
The ICC on Monday said the two trials would not clash, after Mr Kenyatta warned that the constitution prevented the two men from being abroad at the same time.
The president is due to go on trial in November.
The judges at The Hague have indicated the two cases could be heard alternately – in blocks of four weeks.
On Thursday, Kenya’s parliament passed a motion calling for the country to withdraw from the ICC.
The court said the cases would continue, even if Kenya withdrew.
The ICC was set up in 2002 to deal with genocide, crimes against humanity, war crimes and the crime of aggression.