Sudan's security services are holding opposition figures and other detainees without trial, denying medical care to some who need it urgently, a U.N. human rights expert said on Sunday after a visit.
Encouraged by revolutions that have unseated rulers in Egypt, Libya and Tunisia, pro-democracy activists have staged a wave of small protests against veteran ruler Omar Hassan al-Bashir, in power since 1989.
Sudan's National Intelligence and Security Services (NISS) have clamped down hard on street protests in Khartoum and other cities, and authorities have refused to give any details of arrests.
"I am concerned about the arrest and detention of political opposition figures and other individuals by the NISS," said human rights expert Mashood Adebayo Baderin, giving no details on the detainees.
"I urged the government to release (them) or promptly charge them with recognisable offences and bring them before a court of law," Baderin said after meeting U.N. and government officials as well as non-governmental groups.
Baderin, a Nigerian asked by the U.N. Human Rights Council to assess the situation in Sudan, had made his first visit in June.
In a statement released by the United Nations, he said the government must tackle abuses by the security services, which usually tolerate no street protests or critical media articles.
"I must emphasise that violation of human rights by the NISS has been raised consistently by most stakeholders I met during this visit and I urge the government to take this matter seriously," Baderin said.
He also criticised authorities for closing several independent think tanks, despite a call in his last report for civil society groups to be allowed to operate freely.
There was no immediate comment from the government, which routinely denies human rights violations by the authorities.
In contrast to his first trip, Baderin was this time allowed out of Khartoum and visited the western region of Darfur, scene of a decade-long rebellion by mainly non-Arab tribes against a government that they accuse of neglecting them.
He said major challenges existed for human rights in Darfur despite a "relative improvement" due to the work of U.N. agencies.
The International Criminal Court has issued arrest warrants for Bashir and other Sudanese officials on charges of masterminding war crimes in Darfur. They deny the charges and refuse to recognise the court.
Human rights groups and the United Nations estimate that hundreds of thousands of people have died in Darfur's conflict. The government says around 10,000 people have been killed.