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Sudan’s military has used chemical weapons on at least two occasions against the paramilitary group it is battling for control of the country, four senior United States officials said on Thursday.
The weapons were deployed recently in remote areas of Sudan, and targeted members of the Rapid Support Forces paramilitaries that the army has been fighting since April 2023. But U.S. officials worry the weapons could soon be used in densely populated parts of the capital, Khartoum.
The revelations about chemical weapons came as the United States announced sanctions on Thursday against the Sudanese military chief, Gen. Abdel Fattah al-Burhan, for documented atrocities by his troops, including indiscriminate bombing of civilians and the use of starvation as a weapon of war.
The use of chemical weapons crosses yet another boundary in the war between the Sudanese military and the R.S.F., its former ally. By many measures, the conflict in Sudan has created the world’s worst humanitarian crisis, with as many as 150,000 people killed, over 11 million displaced and now the world’s worst famine in decades.
“Under Burhan’s leadership, the S.A.F.’s war tactics have included indiscriminate bombing of civilian infrastructure, attacks on schools, markets, and hospitals, and extrajudicial executions,” the Treasury Department said, using an acronym for Sudan’s armed forces.
General al-Burhan responded with defiance: “We are ready to face any sanctions for the sake of serving this nation, and we welcome them,” he told reporters during a visit to El Gezira state.
The U.S. decision is considered a significant move against a figure seen by some as Sudan’s de facto wartime leader, who also represents his country at the United Nations.
Aid groups fear that Sudan’s military could retaliate against the sanctions by further restricting aid operations in areas that are either in famine or sliding toward it. The decision could also reshape broader relations between Sudan and the United States, whose Sudan envoy, Tom Perriello, has been a leading figure in the faltering efforts to reach a peace deal.
Although chemical weapons were not mentioned in the official sanctions notice on Thursday, several U.S. officials said they were a key factor in the decision to move against General al-Burhan.
Two officials briefed on the matter said the chemical weapons appeared to use chlorine gas. When used as a weapon, chlorine can cause lasting damage to human tissue. In confined spaces it can displace breathable air, leading to suffocation and death.
Knowledge of the chemical weapons program in Sudan was limited to a small group inside the country’s military, two of the U.S. officials said, speaking on the condition of anonymity to discuss sensitive security matters. But it was clear that General al-Burhan had authorized their use, they said.
Sudan’s ambassador to the United Nations, Al-Harith Idriss al-Harith Mohamed, said in a text message that Sudan’s military had “never used chemical or incendiary weapons.”
“On the contrary, it’s the militia that used them,” he added, referring to the Rapid Support Forces.
Last week, the United States determined that the Rapid Support Forces had committed genocide in the war and imposed sanctions on its leader, Lt. Gen. Mohamed Hamdan, for his role in atrocities against his own people. The United States also sanctioned seven companies based in the United Arab Emirates that traded in weapons or gold for the R.S.F.
Sudan’s military has been accused of using chemical weapons before. In 2016, Amnesty International said it had credible evidence of at least 30 likely attacks that killed and maimed hundreds of people, including children, in the western Darfur region. The organization published photos of children covered in lesions and blisters, some vomiting blood or unable to breathe.
As the United States debated punitive measures against General al-Burhan last week, the Sudanese authorities announced that they would maintain a major aid corridor through neighboring Chad, a move American officials saw as an effort to avoid the sanctions.
But the evidence of chemical weapons was too compelling to ignore, several U.S. officials said.
The United States detected numerous chemical weapons tests by Sudanese forces this year, as well as two instances in the past four months in which the weapons were used against R.S.F. troops, two of the officials said.
The United States also obtained intelligence that chemical weapons could soon be used in Bahri, in northern Khartoum, where fierce battles have raged in recent months as the two sides compete for control of the capital.
Chlorine was first weaponized during World War I, and its use in combat is prohibited by international law. In the mid-2000s, insurgents in Iraq weaponized chlorine in attacks on U.S. troops. It has also been used in improvised bombs by ISIS fighters and by the Assad regime in Syria.
Officials briefed on the intelligence said the information did not come from the United Arab Emirates, an American ally that is also a staunch supporter of the R.S.F.
Until Thursday, Sudan’s military was riding high. Last weekend, its troops recaptured the key city of Wad Madani, the capital of Sudan’s breadbasket region, where residents praised the soldiers for ending a yearlong occupation under brutal R.S.F. control.
The victory, combined with the American accusation of genocide against the Rapid Support Forces, suggested that Sudan’s military was finally gaining momentum in a war that it had very recently appeared to be losing.
But in recent days, reports have emerged of vicious reprisals by Sudanese troops against suspected R.S.F. collaborators in the area, including torture and summary executions. The United Nations said it was “shocked” by the reports and ordered an investigation into the killings.
Although the use of chemical weapons was a central element in the decision to level sanctions against General al-Burhan on Thursday, the action was also in response to the military’s bombing raids that have killed dozens of civilians at a time, as well as attacks on hospitals and other buildings that are protected under the laws of war.
Two American officials said the United States was caught in a bind when it came to addressing the chemical weapons with sanctions: In order to protect the source and method of the intelligence used to determine that chemical weapons had been used, the United States did not want to reveal details about the strikes, the officials said.
But U.S. officials also wanted to move against General al-Burhan before President-elect Donald J. Trump’s inauguration on Monday. Under U.S. law, Congress must be notified of the discovery of chemical weapons use, and officials said that members of Congress are expected to be briefed on the issue in a classified hearing next month.
In addition to targeting General al-Burhan, the sanctions announced on Thursday also targeted a man described as a Sudanese arms supplier, and a company based in Hong Kong. A U.S. official said the company had been used to supply Sudan’s military with Iranian-made drones.
The decision to impose sanctions received a mixed reaction among conflict observers. John Prendergast, co-founder of The Sentry, a research and investigative group, hailed the sanctions as a “critical” move and called on the European Union to follow suit.
Nathaniel Raymond, executive director of the Humanitarian Research Lab at Yale School of Public Health, questioned if the United States had made the right decision. “It is concerning there have been no ground reports of an incident consistent with the deployment of a gas agent,” he said.
John Ismay contributed reporting.