A battle between rival Sudanese clans near an oil-drilling site killed 150 people and wounded 100 more, state-linked media reported on Thursday.

The fighting in West Kordofan state between two sub-groups of the Misseriya tribe "continued all day because of a land dispute near the oil field," said Mohammed Omer Al-Ansari, a tribal leader.

Sudanese authorities have blocked a Doctors Without Borders (MSF) emergency team from travelling to Darfur to help thousands of recently-displaced people who are barely surviving, said a statement obtained Thursday.

This is the latest obstacle cited by foreign aid workers in the war-torn and impoverished nation where millions need humanitarian assistance.

Sudan's military on Thursday denied one of its helicopter gunships had been shot down in South Kordofan, after rebels released photographs claiming to show the crippled machine.

"No one shot any of our aircraft," Sudanese Armed Forces (SAF) spokesman Sawarmi Khaled Saad told AFP.

The United Nations has launched an internal investigation into allegations that its joint peacekeeping mission in the troubled Darfur region has been covering up crimes by Sudanese forces against civilians.

The United Nations-African Union peacekeeping force UNAMID, which was established in 2007, is tasked foremost with protecting civilians and securing humanitarian aid for Sudan's Darfur, where violence has left nearly 300,000 dead and two million displaced.

Rebels in Sudan's South Kordofan, where fighting intensified in recent weeks, on Wednesday released photographs of a downed helicopter gunship which they said they shot down.

The Sudan's People's Liberation Army-North (SPLA-N) have previously claimed to have downed government aircraft during the three-year war but they have not provided evidence.

The family of a detained Sudanese youth activist, held for 50 days without charge, on Wednesday alleged he has been tortured in detention.

Tajalsir Jaafar, 28, is one of three activists whose condition a United Nations expert raised concerns about last week.

Battles between Sudanese tribal militias armed with machineguns and rocket-propelled grenades have left up to 22 people dead in a border region of Darfur, sources said on Wednesday.

They were the latest skirmishes between the Hamar and Maaliya groups since December.

Muslim "relatives" of a Sudanese Christian woman hiding at the U.S. embassy are taking her to court to try to prove she belongs to their family, a lawyer said Tuesday.

The complainants are the same people who laid an apostasy charge against Meriam Yahia Ibrahim Ishag, 26, said the lawyer, Mohanad Mustafa.

Violence in South Sudan's civil war including the execution of scores of hospital patients is the worst seen for decades and is an "affront to human dignity", Doctors Without Borders said Tuesday.

"The conflict has at times seen horrific levels of violence, including against healthcare facilities," said Raphael Gorgeu, South Sudan chief for Doctors Without Borders (Medecins Sans Frontieres, MSF).

Hundreds of illegal African immigrants began a hunger strike on Monday after Israeli police forcibly broke up a sit-in they were staging along the Egyptian border.

Around 1,000 Africans, mostly from Eritrea and Sudan, had marched Friday to the border and set up a makeshift camp to protest against their "inhuman and unlimited" detention at Holot facility.