NEW YORK • The United States has confirmed the presence of traces of sulphur mustard, a chemical warfare agent, on fragments of ordnance recently used by the Islamic State in Iraq and Syria (ISIS) in attacks in Syria and Iraq, according to two American officials familiar with the results of laboratory analysis of the samples.
The laboratory tests, which were also performed on scraps of clothing from victims, showed the presence of a partially degraded form of HD, also known as distilled sulphur mustard, an internationally banned substance that burns a victim's skin, breathing passages and eyes.
Kurdish officials in northern Iraq and rebels in northern and eastern Syria have both cited multiple attacks this summer during which noxious chemicals were dispersed, including chlorine and another substance that caused burning and respiratory distress, and that they suspected of being mustard or another blister agent.
In some of the most recent episodes, villagers and activists in Marea, a rebel-controlled village north of Aleppo in Syria that has resisted the militants, reported multiple artillery attacks that left civilians with chemical burns.
The ordnance fragments and clothing samples, which had been flown secretly to the US, came from attacks that variously appeared to involve artillery shells, improvised rockets and mortar shells.
A senior American official in Washington said last Friday that testing had confirmed the presence of sulphur mustard in at least four such instances.
"There's no doubt ISIS has used this," the official said.
Both officials spoke on the condition of anonymity because, they said, the laboratory results were not approved for public release.
The attacks occurred in both Iraq and Syria, the officials said, though they did not say which of the suspected attacks had been confirmed as having involved sulphur mustard or whether the artillery attacks on Marea were among them.
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 ISIS' foes in Iraq and Syria lack, and they are worrisome as potential terrorist weapons, even though chlorine and blister agents are typically less lethal than bullets, shrapnel or explosives.
Chlorine is commercially available as an industrial chemical and has been used occasionally by bomb-makers from Sunni militant groups in Iraq for about a decade.
But it is not known how ISIS would have obtained sulphur mustard, a banned substance with a narrow chemical warfare application, the officials said, and it remains part of a puzzle that the US and other governments have not solved.
Both the former government in Iraq and the current government in Syria previously possessed chemical warfare programmes.
Abandoned and ageing chemical munitions produced by Iraq during its war against Iran in the 1980s were repeatedly used in roadside bombs against American forces during the occupation that followed the 2003 American invasion of Iraq.
However, one official said that the types of ordnance linked to ISIS so far have not matched known chemical ordnance in the former Iraqi inventory.
The official said the attacks have been perplexing, as they have been geographically scattered and have varied in their delivery systems, suggesting that ISIS had access to, and was experimenting with, different types of rockets and shells configured to carry chemical warfare agents or toxic industrial chemicals.
NEW YORK TIMES