The Sudanese government has been accused of launching chemical weapon attacks on its own civilians, killing hundreds of people including scores of children, in what would be a dramatic escalation of the Darfur conflict.

Amnesty International says it has compiled the first credible body of evidence to suggest the forces of President Omar al-Bashir bombed swathes of the crisis-hit Jebel Marra region with chemical agents.

The charity has released before-and-after satellite images, photographs of horrific burn wounds on children and evidence from more than 200 interviews, and called for a United Nations investigation.

Chemical weapons attacks on the African continent in the post-war era have been extremely rare, and even the accusation that it has carried them out could represent a major setback for Sudan’s improving relations with the international community.

But it also serves to highlight the ongoing armed conflict in Darfur that, since the peak of the violence and international attention in 2003, has continued to rage more or less unnoticed.

Satellite imagery from March 2015 (L) and April 2016 shows the village of Karmal has been almost completely razed by fire. Only a few thatched roof tukuls, on the outer edges of the village (R), appear undamaged (Amnesty International)

With the exception of Egypt and South Sudan, all African states have signed the Chemical Weapons Convention committing them to destroy any stockpiles.

Using chemical weapons for anything other than a specific set of military goals, let alone on civilians, is a war crime.

Yet between January and the most recent alleged incident earlier this month, Amnesty International says it has recorded at least 30 likely chemical weapons attacks on Darfur civilian populations.

Those attacks alone have killed around 200 to 250 people, the charity said, with many – possibly even the majority – being children. Countless others have suffered the effects of what appear to be chemical agents, and some described their symptoms to Amnesty over the course of its investigation.

Satellite imagery from November 2015 (L) and 8 April 2016 shows the destruction of the western part of Nuoguey village (top of image), while the eastern half remains relatively intact (Amnesty International)

“Several bombs fell around the village and in the hills,” a mother in her thirties from the village of Burro told the charity. “Most of my kids are sick from the smoke of the bombardment. They got sick on the day of the attack. They vomited and they had diarrhoea, they were coughing a lot [and] their skin turned dark like it was burned.”

“This is first documented, substantial evidence of chemical weapons use inside the Darfur region,” the report author Jonathan Loeb told The Independent.

“We spoke with scores of survivors and people who cared for them about these alleged chemical weapons attacks, and they all said that the alleged chemical was released by bombs or rocket fire.

These bombs and rockets unequivocally came from Sudanese government forces, that we know beyond doubt. There are no other armed actors in the area with any air force [capable of these attacks].”

Amnesty International said it had shared all of its video, photographic and testimonial evidence with two independent chemical weapons experts, and said both concluded that the injuries shown could not have been produced by conventional weapons.

This child's right arm shows large roughly circular lesions showing apparent scarring (Amnesty International)

These lesions are not inconsistent with exposure to sulfur mustard or a similar chemical-warfare-agent vesicant (Amnesty International)

The (partially censored) buttocks of this victim in particular exhibit crops of large, often semi-umbilicated lesions. Scattered nodules or papules are present on the upper thighs (Amnesty International)

The charity is calling on the Organisation for the Prohibition of Chemical Weapons (OPCW) to undertake an investigation into its allegations. Only an on-the-ground probe with access to soil samples, urine samples and weapons fragments can conclusively confirm a chemical weapons attack took place.

“The scale and brutality of these attacks is hard to put into words,” said Tirana Hassan, Amnesty’s director of crisis research. “The images and videos we have seen in the course of our research are truly shocking; in one a young child is screaming with pain before dying; many photos show young children covered in lesions and blisters. Some were unable to breath and vomiting blood.

“The fact that Sudan’s government is now repeatedly using these weapons against their own people simply cannot be ignored and demands action.”

The Bashir government has blocked all access to the Jebel Marra region of Darfur, including to humanitarian groups and even the UN peacekeeping force which is operating elsewhere in the country.

President Omar al-Bashir (AP)

But Amnesty said satellite images showed 171 villages had been destroyed or damaged in the last eight months alone, part of a large-scale military offensive launched in January against the Sudan Liberation Army (SLA), which the government accuses of ambushing military convoys and attacking civilians.

Sudan is currently subject to an arms embargo in relation to human rights abuses in the Darfur region. Yet a report by a UN monitoring panel this week found the government continues to violate the sanctions imposed on it, leading Human Rights Watch to declare the measures “now exist in name only”.

But in a rare international media interview earlier this year, President Bashir denied any abuses had taken place in the mountains of Jebel Marra since the start of the government offensive.

He told the BBC: “All these allegations are baseless, none of these reports is true.

“We challenge anyone to visit the areas recaptured by the armed forces, and find a single village that has been torched.

“In fact, there hasn't been any aerial bombing,” he said.

In a lengthy response to Amnesty's report, Sudanese justice minister Awad Hassan Elnour insisted humanitarian access was available for "all relevant actors" to Jebel Marra and other affected regions.

He said a government committee had interviewed people displaced due to the fighting, and "all stated they left their villages in Jebel Marra voluntarily", adding that they "replied in the negative when asked if they had been exposed to any attack during their movement".

Elnour suggested those who gave evidence to Amnesty were "supporters of the Abdel Wahid [rebel group] or influenced by fear", calling their testimony "unreliable, contradictory and unsubstantiated".

And the minister categorically denied the use of chemical weapons in the region, saying the government was "very astonished to hear this accusation", which it "categorically repudiates".