South Africa's last white president does not have to testify in the trial of 22 people accused of plotting to overthrow the government, a judge has ruled.
De Klerk won a Nobel Peace prize with Nelson Mandela
Judge Bernard Ngoepe said attempts by the defence to call FW de Klerk as a witness were an "abuse of the court process".
The defendants had wanted Mr de Klerk to testify about the legitimacy of South Africa's current government and the non-racial constitution, which they argue, is invalid.
They say the new constitution was not approved by the white electorate before it was introduced in 1994.
The prosecution says the accused, who are alleged to be members of a far-right supremacist organisation, the Boeremag or Afrikaner Force, were involved in several attacks on government installations.
They face a total of 42 charges, including high treason, murder, attempted murder, terrorism and the illegal possession of weapons.
They are accused of the murder of Claudia Mokone who was killed in a bomb blast in the black township of Soweto last December.
Prosecutors say they also conspired to kill Nelson Mandela by blowing up a car transporting the former president to a public event.
The accused said the current government was unconstitutional
Thirteen of the men decided to challenge the court's jurisdiction.
They said the post-apartheid constitution is invalid because white voters were not consulted before its approval.
But Judge Ngoepe dismissed their request to make Mr de Klerk testify about the transfer of power.
"The real issue to be decided by the trial court is... whether it is possible for a section of the population in a unitary state not to be bound by the constitution of the country," he said.