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 refugees 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.

It follows the Trump administration's most vocal intervention to date in the Sudan civil war, with Secretary of State Marco Rubio at the G7 summit demanding international action to halt the supply of weapons to the RSF paramilitaries - plus strongly worded criticism for some nations.

The US is one of the so-called Quad of countries working for an end to the crisis, together with the UAE, along with Egypt and Saudi Arabia who are allies of Sudan's military-led government. The bloc recently proposed a three-month humanitarian truce, followed by a permanent ceasefire and a nine-month transition to civilian rule.

Rubio, in what was widely regarded as a reference to the UAE alleged backing of Sudan's rebels, said on Wednesday: We know who the parties are that are involved [in weapons supply]... That's why they're part of the Quad along with other countries involved.

The UAE, which has long denied supporting the RSF, replied in a statement on Thursday saying it was alarmed by the heinous attacks against civilians by RSF forces in el-Fasher and accused the Sudanese army of starvation tactics, indiscriminate bombardment of populated areas, and the reported use of chemical weapons. These are accusation the Sudanese army has previously rejected.

A furious denial also came from the RSF, denouncing what it called all biased statements against them and attempts to scapegoat it in order to cover up the army's rejection of the truce.

The RSF waited until it had captured el-Fasher before announcing that it was agreeing to the truce. Sudan's army says it objects to the UAE's presence in the Quad but will still consider the proposal.

In the meantime, there has been no let-up in the fighting.

Only a small fraction of the population has managed to flee el-Fasher, where massacres are said to have take taken place. Piles of bodies on the ground and blood-stained earth are visible from space in satellite imagery.

The flow of weapons into Sudan during this war has been analysed by various experts.

Amnesty International says it has found evidence of weapons manufactured in Serbia, Russia, China, Turkey, Yemen and UAE being used in Sudan.

The smuggling route is often via the UAE, through to Chad, then into Darfur - according to a leaked report by UN experts.

The UAE in particular is accused of providing arms and support to the RSF, who in turn are accused of using the UAE as a marketplace for illicit gold sales.

On Wednesday, Rubio pointedly said assistance to the RSF isn't just coming from some country that's paying for it - it's also coming from countries that are allowing their territory to be used to ship it and transport it.

He also said he did not want to diminish the involvement of other actors in the conflict, saying that includes potentially the Iranians, at least money and weapons being flown into the other side, meaning to the Sudanese army.

All parties deny these allegations.

A fortnight ago, the UK government came under fire from its own lawmakers following allegations that British-made weapons were ending up in the hands of the RSF, who were using them to commit atrocities.

In response to one MP's demand to end all arms shipments to the UAE until it is proved that the UAE is not arming the RSF, Foreign Secretary Yvette Cooper said at the time: The UK has extremely strong controls on arms exports, including to prevent any diversion. We will continue to take that immensely seriously.

There has been a UN arms embargo on the RSF's stronghold of Darfur since 2004, but it has not been extended to the rest of the country despite calls from human rights groups.