US Secretary of State Marco Rubio has called for international action to cut off the supply of weapons to Sudan's paramilitary Rapid Support Forces (RSF), who are accused of mass killings in el-Fasher. 

At the end of a G7 foreign ministers meeting in Canada, Rubio said the RSF had committed systematic atrocities, including murder, rape and sexual violence against civilians. 

Sudan's army accuses the United Arab Emirates of propping up the RSF with weapons and mercenaries sent via African nations. The UAE and the RSF have repeatedly denied these allegations.

The RSF has been fighting the Sudanese army since April 2023, when a power struggle between their leaders erupted into all-out civil war.

Rubio's comments are some of the most outspoken so far by the Trump administration about the war in Sudan and the actions of the RSF, but it is not clear how much impact they will have. 

A previous US-backed proposal for a humanitarian ceasefire in Sudan has already been violated by the RSF, even though they agreed to it last week.

El-Fasher was captured last month by the RSF after an 18-month siege, meaning they now control all of the cities in the vast western Darfur region.

Only a small fraction of the population has managed to flee the city, 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. 

Non-Arab groups in the wider Darfur region are being systematically targeted by the RSF in what amounts to genocide, according to the US and humanitarian groups.

At the talks near Niagara Falls on Wednesday, America's top diplomat said women and children had been targeted in acts of the most horrific kind by the RSF in el-Fasher.

Rubio told reporters: "They're committing acts of sexual violence and atrocities, just horrifying atrocities, against women, children, innocent civilians of the most horrific kind. And it needs to end immediately.

"And we're going to do everything we can to bring it to an end, and we've encouraged partner nations to join us in this fight."

However, Rubio stopped short of publicly criticising Abu Dhabi, in spite of evidence that the Gulf state is the RSF's main arms supplier, presented in investigations by the international media that the UN has found credible.

The Trump administration is working for an end to the war together with the UAE, as well as Egypt and Saudi Arabia, who are allies of Sudan's military-led government, collectively known as the "Quad". 

"I don't want to get into calling anybody out at a press conference today, because what we want is a good outcome here," Rubio said on Wednesday, but added pointedly: "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."

In September, the Quad jointly proposed a three-month humanitarian truce, followed by a permanent ceasefire and a nine-month transition to civilian rule.

In a statement on Thursday, the UAE expressed "alarm at the heinous attacks against civilians by RSF forces in El Fasher".

It went on to accuse the Sudanese army of "starvation tactics, indiscriminate bombardment of populated areas, and the reported use of chemical weapons".

These are accusations the army has previously denied.

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.