An independent fact-finding mission will investigate reported mass killings in the Sudanese city of el-Fasher, the UN announced on Friday.

There has been too much pretence and performance, and too little action from the international community in the face of Sudan's devastating civil war, UN human rights chief Volker Türk said at an emergency meeting in Geneva.

It must stand up against these atrocities - a display of naked cruelty used to subjugate and control an entire population, he added, and gave a stark warning to all those fuelling and profiting from the civil war.

More than 150,000 people have been killed and about 12 million have had no choice but to flee their homes.

As part of the investigations, experts will also seek to identify perpetrators in order to hold them to account.

El-Fasher was captured last month by the Rapid Support Forces (RSF) paramilitary group following an 18-month siege. It was the last city in Darfur held by the army and its allies.

The RSF has been accused of targeting non-Arab groups in the city and elsewhere in Darfur - a claim it has denied.

One gruesome feature of this more than two-year-long civil conflict has been the huge volume of footage and photos of horrific atrocities - often seemingly filmed by the culprits themselves, and circulated online. Researchers say this digital evidence will be analysed in a bid to bring the perpetrators to justice.

The people of Sudan, particularly now in el-Fasher, are facing a situation that I never saw before, says Mona Rishmawi, a member of the UN's fact-finding mission on Sudan who has seen the change first-hand over more than two decades.

The scale of the suffering today in Darfur is greater than the Janjaweed militia's genocide in the same region 20 years ago, she told the BBC's Newsday programme. The RSF traces its origins back to the Janjaweed.

Back then, Ms Rishmawi explained, attacks were mainly on villages but now paramilitaries are targeting whole cities and refugee camps housing hundreds of thousands of people.

[There have been] devastating mass killings, rape and torture, disappearances, missing people - and this comes against the background of 18 months of siege and starvation, she said.

A joint G7 statement earlier this week condemned surging violence in Sudan, saying the conflict between the army and the RSF had triggered the world's largest humanitarian crisis.