South Sudan's government has detained scores of opposition figures without issuing arrest warrants or giving them access to lawyers since unrest broke out in a northwestern town in December, Amnesty International said on Wednesday.
South Sudan has struggled to establish the rule of law since it split from Sudan in July in 2011 following a long civil war that left the new country awash with weapons.
Human rights groups regularly accuse its army, an assortment of poorly-trained former guerrilla fighters known as the SPLA, of abuses against civilians, which the government routinely denies.
Ten people were killed in the town of Wau in December when security forces opened fire on a protest against the relocation of a local council headquarters. At least 13 others were killed during unrest that followed the shooting.
Since the violence, the government of Bahr El Ghazal state has detained 100 people, among them opposition figures, civil society activists, journalists and security officers, Amnesty International said in a report.
"Arrests of perceived opponents of the government continue to be carried out," the group said.
"While some of these arrests appear to have a legitimate basis, evidence gathered by Amnesty International shows that many of the arrests were arbitrary and contravene provisions in national and international law," it said.
South Sudan government officials were not immediately available for comment.
Unverified video footage broadcast on Doha-based Al-Jazeera television showed state security personnel opening fire on unarmed protesters during the December protest.
The failure of the authorities to properly investigate the violence has increased tensions in Wau, Amnesty said.
(Editing by Ulf Laessing and Tom Pfeiffer)