WASHINGTON — A top specialist in chemical weapons for the Islamic State who is in American custody in northern Iraq has given military interrogators detailed information that resulted in two allied airstrikes in the last week against the group’s illicit weapons sites, Defense Department officials said on Wednesday (March 9).

The prisoner, an Iraqi identified by officials as Sleiman Daoud al-Afari, was captured a month ago by commandos with an elite American Special Operations force. He was described by three officials as a “significant operative” in the Islamic State’s chemical weapons program. Another official said he once worked for Saddam Hussein’s Military Industrialization Authority.

The Islamic State’s use of chemical weapons in Iraq and Syria has been known, but Mr Afari’s capture has provided the United States with the opportunity to learn detailed information about the group’s secretive program, including where chemical agents were being stored and produced.

Under interrogation, Mr Afari told his captors how the group had weaponised sulfur mustard and loaded it into artillery shells, the officials said. Based on information from Mr Afari, the United States-led air campaign conducted one strike against a weapons production plant in Mosul, Iraq, and another against a “tactical unit” near Mosul that was believed to be related to the program, the officials said.

Pentagon officials refused to publicly acknowledge the capture and interrogation of Mr Afari, saying that they did not want to reveal details of what the American Special Operations team is doing in Iraq. But, “We know they have used chemical weapons in both Iraq and Syria,” a Pentagon spokesman, Capt Jeff Davis, said on Wednesday, referring to the Islamic State. “This is a group that does not observe international norms.”

Captain Davis said “in large doses” the sulfur mustard agent “can certainly kill,” citing a case last year of a Syrian baby who died after a chemical attack unleashed by the Islamic State on her home in northern Syria.

Dozens of people in the northern Iraqi town of Taza suffered from respiratory and skin irritation after a mortar and rocket barrage there by Islamic State militants, in what local officials said on Wednesday was a chemical attack.

“Forty cases have been transferred to Kirkuk General Hospital, with four critical cases among them,” said Mr Muhammad al-Mussawi, the head of the Popular Mobilization Forces in the Kirkuk area, including Taza.

The Islamic State has kept up heavy bombardment of the area around Taza for at least three months. But a local security official, speaking on the condition of anonymity because he was not authorised to brief the news media, said this was the first time a chemical attack on the village was suspected, given the number of people who were ill immediately after the bombardment. He said he believed the attack used chlorine gas, though there was no one to independently confirm that.

The United States has long suspected the Islamic State of using sulfur mustard, a chemical warfare agent, and last year officials said that they confirmed the presence of the mustard gas on fragments of ordnance used in Islamic State attacks in Syria and Iraq. Laboratory tests, which were also performed on scraps of clothing from victims, showed the presence of a partly degraded form of distilled sulfur mustard, an internationally banned substance that burns a victim’s skin, breathing passages and eyes.

Chemical warfare agents, broadly condemned and banned by most nations under international convention, are indiscriminate. They are also difficult to defend against without specialised equipment, which many of the Islamic State’s foes in Iraq and Syria lack. The agents are worrisome as potential terrorist weapons, even though chlorine and blister agents are typically less lethal than bullets, shrapnel or explosives.

It was unclear how the Islamic State obtained sulfur mustard, a banned substance with a narrow chemical warfare application. Both the former government in Iraq of Saddam Hussein and the current government in Syria at one point possessed chemical warfare programs.

Mr Afari was captured last month by a new Special Operations force made up primarily of Delta Force commandos shortly after they arrived in Iraq. They are the first major American combat force on the ground there since the United States pulled out of the country at the end of 2011.

Two weeks after his capture military officials notified the International Committee of the Red Cross, which monitors the treatment of prisoners, that they were holding an Islamic State fighter. The Red Cross acknowledged in a statement on Tuesday that it had visited Mr Afari but gave no other information.

The military’s assertion that Mr Afari was part of Saddam Hussein’s Baathist program in the 1980s is not ironclad, based on details released so far. Mr Afari is believed to be about 50, which would mean he was in his teens or early 20s at the time.

Pentagon officials insist that the United States has no plans to hold Mr Afari or any other prisoners for any length of time, and say that they will be handed over to Iraqi and Kurdish authorities after they have been interviewed. The officials say they do not intend to establish a long-term American facility to hold Islamic State prisoners, and Obama administration officials have ruled out sending any to the United States military prison at Guantánamo Bay, Cuba.

Until recently, the United States has largely targeted Islamic State fighters with airstrikes. But the 200-member Special Operations team has been assigned to both kill and capture Islamic State operatives, the latter for use in gathering intelligence. Military officials said the team had set up safe houses and worked with Iraqi and Kurdish forces to establish informant networks and conduct raids on Islamic State leaders and other important militants.

Senior Defense Department officials say the model for handling Mr Afari was a Delta Force raid last May, when two dozen American commandos from Iraq entered eastern Syria aboard Black Hawk helicopters and V-22 Ospreys and killed Abu Sayyaf, described by American officials as the Islamic State’s emir for oil and gas. Abu Sayyaf’s wife, Umm Sayyaf, was captured and taken to a screening facility in northern Iraq, where she was questioned and detained. American forces seized laptops, cellphones and other materials from the site.

After being held for three months by the American authorities and providing them information, officials said, Umm Sayyaf was transferred in August to Kurdish custody. Last month, the Justice Department filed an arrest warrant charging her with conspiring to provide material support to the Islamic State in an offence that officials said resulted in the death of Kayla Mueller, the American aid worker who was killed in Syria in February 2014. THE NEW YORK TIMES