"Something new for me," he tweeted.
"So far, as the rest of the international community, I believed that Iran was a victim of the use of chemical weapons by Sudan [Saddam] Hussein," he added.
"Why did the US keep this information secret, if it is true?" Ulyanov asked.
In another tweet on the same day, he addressed a former Trump National Security official Richard Goldberg, writing: "Your reference to the report of the US Department of State - famous for its biased reports- is not convincing."
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