A fire raged Wednesday at a southern Tehran oil refinery after a leak in a liquefied gas line triggered an explosion, the head of the Iranian capital's crisis team told state television.

More than an hour after the blaze started, flames and thick clouds of black smoke could be seen reaching high into the sky from across Tehran, an AFP correspondent said.

An "accident was caused by a leak from an emergency liquified gas line," triggering "an explosion which caused the start of the fire that we can observe," Tehran crisis team chief Mansour Darajati told state television.

Darajati said that the fire had begun at around 7:30 pm local time (1500 GMT) and that there were "fortunately no deaths at this stage".

According to state news agency IRNA, the stricken refinery has been operational since 1968, has a capacity of 250,000 barrels per day and is owned by the Tehran Oil Refining Company.

A spokesman for the company dismissed "all speculation centring on sabotage at the refinery", according to state television's Telegram channel.

"The accident was caused by a technical problem and we are currently in the process of controlling the fire," he added.

The blaze comes several hours after the Iranian navy announced that one of its biggest vessels -- the Kharg, a fleet replenishment ship -- had sunk in the Gulf of Oman, due to a fire. 

The cause of that blaze has not been publicly identified.