The International Criminal Court has adjourned Kenya Vice President William Ruto's crimes against humanity trial until January 13, the court said on Friday.
President Uhuru Kenyatta and his deputy Ruto are charged by the Hague-based court with fomenting political unrest in which more than 1,100 people were killed and hundreds of thousands displaced following a disputed 2007 election.
The court said in a statement that the case against Ruto and Kenyan radio boss Joshua arap Sang was experiencing "difficulties".
"The witnesses that the defence is ready to examine are not available, and as regards the witnesses that the prosecution has contacted and are ready to testify, the defence is not ready to cross-examine them," the court said.
The cases have been dogged with problems and delays, including witness withdrawal and Kenya's campaign to have the cases put on hold.
Arguments include allegations that the court is targeting Africans and that Kenya's leaders need to be available to tackle Al-Qaeda-linked militants who have turned neighbouring Somalia into a major global jihadist hub.
The Shebab group carried out an attack on a Nairobi mall that killed at least 67 people in September in retaliation for Kenya's involvement in Somalia.
Hearings in the Ruto and Kenyatta trials are expected to alternate "because of the common personnel and logistical support for the two cases," the court said in its statement.
The Kenyatta trial is to begin on February 5.