"If we want to do something, we have to do it quickly," he said in a video broadcast on Iranian state television.
"If it happens two or three months later, it won't have the same effect."
Human rights organizations have warned that one of the thousands of Iranians arrested in recent days, 26-year-old Erfan Soltani, will be executed as early as Wednesday.
US President Donald Trump has warned Iran of retaliation if it begins executing protesters.
"If they do something like that, we will take very strong action," he told CBS News on Tuesday.
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