By Alastair Leithead BBC correspondent in Johannesburg

Bomb attacks were part of the alleged plot

The state is arguing that they were all members of the Boeremag or Afrikaaner Force which carried out a series of bomb attacks last year and planned to assassinate Nelson Mandela.

The trial in Pretoria's Palace of Justice is surrounded by the highest security for a court case in more than a decade.

And the venue is historically significant - 40 years ago Mr Mandela was jailed for life in the same courtroom for conspiracy to topple the government, along with other anti-apartheid activists.

The defendants are charged with high treason, with alternative charges of terrorism and sabotage, over an alleged plot to overthrow the government through a series of bomb attacks last year.

They are said to have planned to destabilise the country and then stage a coup and recreate a whites-only Afrikaaner state.

Also among the 43 charges are murder and attempted murder, involving a plan to assassinate former Mr Mandela by blowing up his car.

The state has more than 360 witnesses and 600 witness statements, and the trial is expected to last two years.

It is thought it will become a trial within a trial as the men challenge the legality of the court to hear their case, and it will be littered with postponements and adjournments.

At today's hearing, the trial was postponed for a week, following legal arguments.