Sudan’s military has used chemical weapons on at least two occasions against a paramilitary group it is fighting for control of the country, four senior United States officials said Thursday.

The weapons were recently deployed in remote areas of Sudan, targeting members of the Rapid Support Force paramilitary force that the army has been fighting since April 2023. But US officials worry the weapons could soon be used in densely populated areas of the capital, Khartoum.

The revelations about chemical weapons came when the United States announced sanctions on Thursday against Sudan’s army chief, General Abdel Fattah al-Burhan, for documented crimes by his troops, including the indiscriminate bombing of civilians and the use starvation as a weapon of war.

The use of chemical weapons crosses another line in the war between the Sudanese army and the RSF, 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, more than 11 million displaced and now the world’s worst famine in decades.

“Under Burhan’s leadership, the SAF’s war tactics included indiscriminate bombing of civilian infrastructure, attacks on schools, markets and hospitals, and extrajudicial executions,” the finance ministry said, using an acronym for the Sudanese Armed Forces.

General al-Burhan responded with defiance: “We are ready to face all sanctions to serve this people and we welcome them,” he told reporters during a visit to El Gezira state.

The US decision is seen as a significant move against a man seen by some as Sudan’s de facto warlord, who also represents his country at the United Nations.

Aid groups fear the Sudanese military could retaliate against the sanctions by further curtailing aid operations in areas that are either starving or sliding towards it. The decision could also reshape broader relations between Sudan and the United States, whose envoy to Sudan, Tom Perriello, has been a leading figure in the faltering efforts to reach a peace deal.

Although chemical weapons were not mentioned in Thursday’s official sanctions notice, several US 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 permanent damage to human tissue. In confined spaces, it can displace breathable air, leading to suffocation and death.

Knowledge of Sudan’s chemical weapons program was limited to a small group within the country’s military, two U.S. officials said, speaking on condition of anonymity to discuss sensitive security issues. But it was clear that General al-Burhan authorized their use, they said.

Sudan’s ambassador to the United Nations, Al-Harith Idriss al-Harith Mohamed, said in a text message that the Sudanese military “has never used chemical or incendiary weapons.”

“On the contrary, they were used by the militia,” he added, referring to the Rapid Support Force.

last week, determined by the United States that the Rapid Support Force committed genocide in the war and imposed sanctions on its leader, Lt. Gen. Mohamed Hamdan, for his role in crimes against his own people. The United States also sanctioned seven companies based in the United Arab Emirates that traded arms or gold to the RSF

The Sudanese army has previously been accused of using chemical weapons. In 2016 Amnesty International said he had credible evidence of at least 30 possible attacks which killed and maimed hundreds of people, including children, in the West Darfur region. The organization published photos of children covered in wounds and blisters, some vomiting blood or unable to breathe.

As the United States discussed punitive measures against General al-Burhan last week, the Sudanese authorities announced that they would maintain the main aid corridor through neighboring Chada move that US officials saw as an attempt to avoid sanctions.

But the evidence of chemical weapons was too compelling to ignore, several US officials said.

The United States has detected numerous chemical weapons tests by Sudanese forces this year, as well as two cases in the past four months in which the weapons were used against RSF forces, two officials said.

The United States has also received intelligence that chemical weapons may soon be used in Bahri, in northern Khartoum, where fierce battles have raged in recent months as two sides vie for control of the capital.

Chlorine was first used as a weapon during the First World Warand its use in combat is prohibited by international law. In the mid-2000s, insurgents in Iraq used chlorine as a weapon in attacks on American troops. It was also used in improvised bombs by ISIS fighters and by the Assad regime in Syria.

Officials familiar with the intelligence said the information did not come from the United Arab Emirates, a US ally that also strongly supports the RSF.

Until Thursday, the Sudanese army was at its peak. Last weekend, his troops recaptured the key town of Wad Madani, the capital of the Sudanese granarywhere residents praised the soldiers for ending a year-long occupation under brutal RSF control.

The victory, combined with a US charge of genocide against the Rapid Support Force, suggested the Sudanese military was finally gaining momentum in a war it had recently appeared to be losing.

But in recent days there have been reports of brutal reprisals by Sudanese troops against suspected RSF collaborators in the area, including torture and summary executions. The United Nations said it was “shocked” by the reports and ordered an investigation into murders.

Although the use of chemical weapons was a central element in the decision to impose sanctions on General al-Burhan on Thursday, the action was also in response to military bombings that killed dozens of civilians at once, as well as attacks on hospitals and other buildings protected by wartime laws. laws.

Two U.S. officials said the United States was caught in a quandary when it came to chemical weapons sanctions: To protect the source and method of intelligence used to determine that chemical weapons were used, the United States did not want to disclose details of the strikes, they said. officials.

But US officials also wanted to move against General al-Burhan before the inauguration of President-elect Donald J. Trump on Monday. Under US law, Congress must be notified of the discovery of the use of chemical weapons, and officials said members of Congress were expected to be briefed on the matter at a confidential hearing next month.

In addition to General al-Burhan, the sanctions announced Thursday also target a man described as a Sudanese arms supplier and a company based in Hong Kong. A US official said the company was used to supply the Sudanese military with Iranian-made drones.

The decision to impose sanctions caused different reactions among observers of the conflict. John Prendergast, co-founder of The Sentry, a research and research 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 Laboratory at the Yale School of Public Health, questioned whether the United States made the right decision. “It is concerning that there have been no reports of an incident consistent with the deployment of a gas agent,” he said.

John Ismay contributed reporting.