Hundreds of civilians in Darfur, including young children and babies, have been killed or injured in a devastating wave of chemical-weapon attacks by Sudanese military forces this year, a new study by Amnesty International says.

Government forces are believed to have launched at least 30 chemical attacks, delivered by bombs and rockets, over the past eight months in the Jebel Marra region of Darfur, including an attack as recently as Sept. 9, the Amnesty report says.

Sudan's President Omar al-Bashir is already facing charges of war crimes and genocide for his actions in Darfur. He was indicted on those charges by the International Criminal Court in The Hague in 2009 and 2010 but has refused to surrender.

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The use of chemical weapons is considered a war crime and has been banned for decades. But dozens of disturbing photos, released by Amnesty, show children with blisters and lesions that are consistent with chemical-weapons attacks. About 200 to 250 people, mostly children, may have died in the attacks so far, Amnesty said.

The 99-page report, released on Thursday, is based on satellite images, expert analysis of photos and more than 200 interviews with survivors and caregivers. It was written and researched by Canadian human-rights activist Jonathan Loeb, who works as Amnesty's senior crisis adviser for Sudan.

Two independent chemical-weapons experts, who reviewed the photos and testimony from survivors, told Amnesty that the evidence strongly suggested the victims were exposed to blister agents such as sulphur mustard or nitrogen mustard, which are chemical-warfare agents.

Survivors told Amnesty they saw a noxious-smelling smoke, which changed colour, after bombs were dropped on their villages by Sudanese military airplanes. Amnesty said the description is consistent with chemical weapons.

Many survivors suffered injuries that included respiratory problems, blindness and other eye problems, severe gastrointestinal conditions and "blistering and rashes on skin which reportedly hardened, changed colour and fell off," Amnesty said. Many victims had no access to medical treatment and were treated only with a combination of local herbs, salt and lime.

The region of Jebel Marra, one of the last remaining rebel strongholds in Darfur, has been the target of a government offensive since January. More than 250,000 people have fled their homes in the region since January because of the fighting, United Nations agencies have said.

Independent media and human-rights groups are barred from the region, so information has been sketchy. With the help of local intermediaries, Amnesty conducted telephone interviews with 235 survivors of the alleged chemical attacks.

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"The scale and brutality of these attacks is hard to put into words," Amnesty crisis-research director Tirana Hassan said in a statement.

"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."

One woman in the village of Burro said she saw several bombs discharging black smoke that turned blue. "Most of my kids are sick from the smoke of the bombardment," she told Amnesty. "They vomited and they had diarrhea. … Their skin turned dark, like it was burned."

Chemical weapons are banned because "the level of suffering they cause can never be justified," Ms. Hassan said. "It is hard to exaggerate just how cruel the effects of these chemicals are when they come into contact with the human body."

In addition to the chemical attacks, the military campaign has destroyed or damaged 171 villages in Darfur, and many people died from starvation or dehydration after the attacks, Amnesty said.