The accused, who include retired military, security and police officers, were arrested at their homes in July on charges of plotting to sabotage the government and planning political assassinations. They deny the charges.

Their trial was due to start earlier this month but was postponed.

"The court is starting on Sunday," said lawyer Muez Hadra. "We will hear the prosecutor and then the lawyers will begin the cross examination."

Hadra said three of the accused -- two retired army men and one still in service -- were being held in army headquarters away from the others in Kober prison, bringing the number to face trial to 30. Earlier officials said 28 had been arrested.

The defence team said the case against them was weak after the head of the opposition Umma Party for Reform and Renewal, Mubarak al-Fadil, was released due to a lack of evidence to support charges he was the coordinator of the attempted coup.

Fadil's party secretary-general Abdel Jalil al-Basha and the deputy secretary-general of another opposition Democratic Unionist Party (DUP) Ali Mahmoud Hassanein are still detained.

After his release Fadil said the legal system in Sudan needed reform but that he expected the accused to be released as the charges were baseless and confessions had been obtained under torture.