Kenyan President Uhuru Kenyatta's lawyers have asked the International Criminal Court (ICC) to abandon his trial even before it starts.
In a written request to The Hague-based court, they said they had evidence that defence witnesses had been intimidated.
The lawyers also claimed that prosecution witnesses had been trying to pervert the course of justice.
Mr Kenyatta is accused of crimes against humanity during the 2007 post-election violence – a claim he denies.
Some 1,200 people died and 600,000 were forced from their homes during the conflict.
Mr Kenyatta's trial is set to start in The Hague on 12 November.
Deputy President William Ruto is also on trial – he is the first serving senior government official to be tried by the ICC.
The prosecution has previously said that its witnesses were being intimidated – some of whom have refused to testify.
Last week, the court issued an arrest warrant for Kenyan journalist Walter Barasa on suspicion of offering bribes to prosecution witnesses – charges he denies.
Mr Kenyatta's lawyers filed the 38-page request on Thursday, calling for a "permanent stay of proceedings".
"The defence is in possession of substantial evidence of a serious, sustained and wide-ranging abuse on the process of the court," the document said.
It also said there was evidence to prove that three prosecution witnesses and one intermediary were involved in a serious and sustained conspiracy to pervert the course of justice.
The defence lawyers also accused the prosecution of "presiding over an utterly corrupt and dishonest case".
The prosecution is now expected to respond in writing to the defence's claims, and the ICC could then order a hearing into the allegations.
The timing of the claims could not be worse for the ICC, as the African Union will discuss a mass withdrawal from the court at talks on Friday and Saturday, the BBC's Anna Holligan reports from The Hague.
So far all the court's indictments have been against Africans, and many leaders on the continent accuse the ICC of unfair bias.
Human rights groups have been campaigning to convince them not to leave the ICC, but the allegations from the defence lawyers will do little to restore faith in the controversial court, our correspondent says.
Mr Kenyatta has twice failed to defer – or indefinitely postpone – the case from the world court.
On Wednesday, Nairobi requested that the trial be held via video link.
Foreign Minister Amina Mohamed said Mr Kenyatta had fully co-operated with the ICC, but the circumstances had changed since he won the presidency in March.
"Today he is the head of state of the republic. It's going to be the first time that a sovereign head is brought before any court of any kind, not just here but anywhere in the world," the minister said.
Mr Ruto had to ask for his trial to be adjourned last month so he could return home to deal with the Westgate shopping centre terror attack.
He was given a week's delay – less than he had requested.