"Two people died on Tuesday night, in addition to two others killed in recent days," said Hassan Nouri, deputy director of the country's emergency services.
Nouri said some 3,450 people had been injured in this year's festivities.
The fire festival, an ancient Zoroastrian tradition, predates Islam and is celebrated on the last Wednesday of the Persian calendar, which ends this year on March 20.
The tradition remains popular among Iranians, who light and jump over bonfires while singing songs to mark the arrival of spring.
At this year's celebrations, young people set off fireworks as others lobbed gas-filled bottles into fires, causing explosions.
But following police warnings, the number of festival-related deaths and injuries fell this year in comparison to 2017, when 16 people died, Nouri said.
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