Nairobi/Khartoum  - Sudan is holding hundreds of people without charge and trying them before "sham courts" for their alleged roles in a rebel attack on Khartoum in May, Amnesty International said Monday after eight people were sentenced to death.

Over 100 people are facing charges in Sudan's Anti-Terrorism Special Courts, which on Sunday sentenced eight alleged members of the rebel Justice and Equality Movement (JEM) to death.

The international human rights watchdog said the fate and whereabouts of many of those held was still unknown, adding it had received reports of torture and extra-judicial executions.

The courts have sentenced almost 40 people to death in relation to the attack and the United Nations has already expressed concern over the courts.

"Sudan's Anti-Terrorism Special Courts are nothing but a travesty of justice," Tawanda Hondora, Africa Deputy Director at Amnesty International, said in a statement.

"Those trials were clearly unfair and now Sudan is preparing to try yet more people with this system," Hondora added.

Over 200 died and many more were injured on May 10 when rebels attacked Omdurman, which sits just over the River Nile from Khartoum. The rebels were only just stopped from entering Khartoum itself.

The attack was the closest rebels had come to the capital, and led to Sudan breaking off diplomatic ties with neighbouring Chad, which Khartoum accused of supporting the rebels.

The accusations came on the day Sudanese President Omar al-Bashir was due to travel to Istanbul for a summit of African leaders - his first trip abroad since the chief prosecutor of the International Criminal Court (ICC) accused him of genocide.

ICC Chief Prosecutor Luis Moreno-Ocampo asked for an arrest warrant, accusing al-Bashir of war crimes in Sudan's restive western Darfur province.

The UN says up to 300,000 people have been killed and 2.5 million displaced by five years of conflict in Darfur. (dpa)