Analysis by BBC Verify of videos showing fighters boasting of a massacre and later mocking survivors has identified those responsible as apparently belonging to Sudan’s paramilitary Rapid Support Forces (RSF).

The BBC has confirmed that at least 80 people died in the October attack on al-Seriha in Gezira state, with the UN reporting that the death toll could be as high as 124. An eyewitness told BBC Verify he saw unarmed civilians gunned down by fighters at close range as they tried to flee.

The massacre appears to have been prompted by the defection of a senior RSF commander in Gezira state to the country’s armed forces.

In a statement to the BBC, an RSF spokesman denied its fighters were involved in the killings adding that “the Rapid Support Forces work to protect civilians and promote security and peace, and not to target them.”

The brutal conflict, a 20-month power struggle pitting Sudan’s military authorities against their former RSF allies, has been condemned by human rights groups for widespread atrocities committed by both sides.

Warning: This story contains detailed descriptions of killings and images of dead bodies, which some readers may find distressing.

On 20 October, the Sudanese military announced that Abu Aqla Keikal, a senior commander with the RSF in Gezira state, had defected to them along with a sizeable number of his forces.

Keikal’s decision to return to the Sudanese army, where he’d served before the war, was hailed as a major propaganda success, and other RSF soldiers were urged to do the same as part of a wider amnesty offer.

Shortly after Keikal’s defection, fighters launched a series of at least 69 reprisal attacks on towns and villages in Gezira state between 20 October and 4 November, according data recorded by the war monitoring organisation Armed Conflict Location and Event Data (ACLED).

BBC Verify has investigated one of these attacks in detail, using eye-witness testimony, satellite imagery, video footage and photographs, to understand what happened.

Mohammad Ismail was attending dawn prayers at a local mosque on 25 October when he heard the fighters approaching the outskirts of al-Seriha, a town of around 15,000 people, 90km (60 miles) south of Sudan’s capital, Khartoum.

He told the BBC that he ran home to protect his family as the violence erupted all around.

Gunmen had climbed up onto a mosque, he said, and were shooting “at whatever moved” below.

Many people were shot while trying to escape, he said. Others were gunned down at close range in the fields surrounding the town. Many of his family members were among the dead.

BBC Verify has obtained a series of videos filmed by fighters themselves, boasting of their actions and calling out to Keikal, the former RSF commander, to see for himself what they were doing to the people from his area.

In one, troops with RSF insignia are seen celebrating their attack on the town and of killing locals. The circular insignia seen on their right shoulders, also visible in some other clips, has a black outline, a curved representation of the Sudanese flag and a round logo above this – the symbol used by the RSF.

We have confirmed that this video was filmed in al-Seriha by comparing buildings and other elements within the videos with satellite imagery of the town.

In one of the videos, a fighter displays his wristwatch to the camera, showing the date as 25 October – and repeating it out loud – the date of the massacre in al-Seriha.

Mr Ismail also told the BBC that when they came to the town, he recognised some of the fighters involved in the attack as former residents who had signed up to fight with the RSF.

He also said he saw two commanders known to be senior RSF leaders in the area. BBC Verify put images of some RSF fighters through facial recognition software in an attempt to identify the individuals, but these searches returned no matches.

The troops left locals in no doubt that the massacre had been carried out in response to Keikal’s defection.

In one video a guard says in Arabic: “Keikal … look these are your people.”

We were able to match landmarks in this video such as trees and the shape of nearby buildings seen in the videos to satellite images of al-Seriha.

In a further video – which couldn’t be geolocated but first appeared online on 26 October – men wearing military fatigues with RSF insignia talk about Keikal’s defection and refer to “traitors” in Gezira state. They specifically mentioned al- Seriha, adding that the town would get what it deserved.

At several points in the video, they refer to themselves using the Arabic word “ashawis” meaning the “brave ones”, a term used by RSF fighters to identify themselves.

When BBC Verify approached the RSF for comment, they denied those seen in the clips were their troops. “You can easily obtain a Rapid Support Forces uniform and wear it… then commit crimes against civilians, to criminalise the Rapid Support Forces,” a spokesperson for the group said.

While it’s not possible to rule this out, the BBC has seen three separate videos filmed by the fighters themselves, in which RSF insignia can be seen on the uniforms of those involved.

A report by Human Rights Watch into the attacks on al-Sehira and other towns in Gezira state since Keikal’s defection on 20 October, identified the RSF as the perpetrators.

On 29 October, the UN issued a statement condemning the killings in al-Seriha and other towns in Gezira state and identifying the RSF as being responsible for these attacks.

The BBC has obtained four separate videos of the aftermath of the attack on al-Seriha. They are very graphic and show bodies lined up in the courtyard of a mosque, covered with shrouds and blankets. The earliest versions of these videos appeared online on 26 October.

BBC Verify has established that the image below was taken in the courtyard of the mosque by matching key features, including the steel gate and a satellite dish in the background, to an image of the mosque from Google maps.

BBC Verify studied the video and photographic evidence, counting at least 82 bodies laid out on beds or on the floor.

The UN has said that 124 people died the reprisal killings in al-Seriha. A local civil society group, the Gezira Congress, says that figure could be as high as 140.

Another piece of evidence uncovered by the BBC Verify investigation is the appearance of freshly-dug earth mounds in the town cemetery.

Mr Ismail had told us that a mass grave had been dug in the graveyard.

In satellite photos captured after the attack, these mounds can be seen in a previously unused section of the cemetery. They are not present in satellite images taken in May.

Nathaniel Raymond, Executive Director at the Yale’s Humanitarian Research Lab told the BBC that in a separate image taken on 30 October, the graves appear to have been recently dug given the distinct shape of the mounds and the colour of the surrounding earth. In the graphic above, we’ve shown a satellite image from 6 December which more clearly shows the cemetery.

“These two indicators tell us that the mounds had not been there for likely more than a few days because the edges of the mounds over time will smoothen and become more blurry because of wind and dust,” he said.

While the BBC cannot verify how many people may be buried in the new section of the cemetery, the size of the earth mounds measured against the nearby white building suggests many bodies could have been buried there.

Once the initial shooting was over and the troops had taken control of the town, the surviving men were rounded up and detained.

BBC Verify has obtained videos of these detentions and abductions.

In one, at least 60 people can be seen sitting or standing against a wall being watched by the armed fighters.

Some of the captives appear to be elderly, and many are wearing what seem to be bloodstained white robes.

At one point in the video, the fighters taunt their captives, calling them dogs and making animal noises.

“Say baa, you dogs, say baa, say baa. You dare again to take up arms, don’t mess with the Rapid Support Forces.”

BBC Verify has confirmed this was filmed at the north-western part of the town by matching distinctive features shown on satellite maps. In particular, there is a corrugated iron structure visible which can also be seen on satellite imagery captured on 30 October.

Others are seen walking in a line with their arms raised. Footage later shows the fighters mocking their captives, with residents forced to make animal noises while the fighters laugh and look on.

Another group of men were later marched past the fighters with their hands behind their backs.

As the group file past, one fighter recognisable from earlier clips again mocks the men.

“Did we defeat al-Seriha,” the fighter asks the captives, before repeatedly saying: “Did we do well?”

Elmubir Mahmoud, secretary-general of the Gezira Congress, told the BBC the fighters took 150 hostages away with them after they left the town. He said that at least 11 captives – including a three-year-old girl – have since been killed. BBC Verify cannot confirm this.

But testimony given to us by town resident Mohammad Ismail suggests that survivors were forced to pay ransoms for the release of their family members. He said their captors had demanded between US$100 and US$1,000.

The activities of the RSF and the Sudanese military in Gezira state have attracted international condemnation, with the UN and human rights groups expressing outrage.

In a statement, the US Ambassador to the UN Linda Thomas-Greenfield urged countries to cease providing arms to both sides of the war. She said supplies were prolonging the conflict.

“The people of Sudan have endured hell,” she said. “They deserve safety, dignity, and justice. They deserve to live.”

Additional reporting by Mohanad Hashim. Graphics by Mesut Ersoz.