ISTANBUL — The poison used in the deadly chemical bomb attack in a rebel-held part of northern Syria this week was the banned nerve agent sarin, the Turkish Health Ministry said in a statement on Thursday.

The statement from Turkey, where many of the stricken Syrians were taken after the assault on Tuesday, was the most specific about the cause.

“According to the results of preliminary tests,” the statement said, “patients were exposed to chemical material (Sarin).”

Western countries have accused the Syrian government of President Bashar al-Assad of carrying out the chemical attack on the town of Khan Sheikhoun in Idlib Province, which left scores dead and hundreds sickened in one of the worst atrocities so far in the six-year-old Syria war.