A huge fire that swept through heavy crude containers at Tehran oil refinery is almost under control.

A huge blaze at the Shaheed Tondguyan Oil Refinery located to the south of the Iranian capital Tehran is almost extinguished after more than 24 hours of battling the fire, says the top government official in the facility.

Hamed Armanfar, who serves as the CEO of refinery, said on Thursday that there were no casualties whatsoever in the fire that began a day earlier in tanks used for storage of heavy oil products.

Fortunately the fire has been fully contained and controlled and it would take one or two hours before we can extinguish the remaining patches, Armanfar was quoted as saying by Oil Ministry’s news service Shana.

The official said that the fire had affected two storage tanks containing slop oil. He said the tanks, situated on the same band wall, had contained 25,000 tons of emulsified crude oil when the fire erupted in the refinery.

The fire began 7.30 pm local time on Wednesday over what officials described as leaks in the tanks. However, an investigation has been launched to determine the exact causes of the incident.

Iranian Oil Minister Bijan Namdar Zanganeh was at the site of fire hours after it erupted. He said the blaze was not significant, adding that the heavy hydrocarbons normally produce thick column of black smoke if they catch fire.

Heavy smoke does not mean that the incident was serious, said Zanganeh in response to claims that authorities were seeking to cover up the incident and its impacts on operations in the refinery.

Both Zanganeh and Armanfar insisted that the blaze had not caused any disruption to production in the refinery, an old oil facility that processes a quarter of million barrels of crude per day.