A major fire that tore through an oil refinery in the Iranian capital had been brought under control on Thursday, but was still not completely extinguished.

The blaze broke out at 7:30 pm (1500 GMT) on Wednesday after an explosion at the facility caused by a leaking gas pipe, sparking an inferno that left 11 people injured, the authorities said.

"The fire at the refinery has been brought under control," the official IRNA news agency reported in the morning, citing Shaker Khafai, spokesman for Tehran Oil Refining Company.

A column of black smoke was still visible over the site of the blaze in mid-afternoon, AFP journalists reported, although it was not as thick as the day before.

"Eleven people, including nine firefighters tackling the blaze, were injured," Mojtaba Khaledi, spokesman for the national rescue service, told AFP. 

Four required hospitalisation, including three firefighters, he added.

Teams of firefighters were seen battling the blaze in footage from the scene broadcast by state television.

The authorities have launched an investigation into the incident.

The refinery is located in a large industrial zone on Tehran's outskirts, only a few hundred metres (yards) from residential areas.

It has been in operation since 1968 and has a capacity of 250,000 barrels per day, according to IRNA.

Industrial accidents are common in Iran.

On May 23, nine people were injured in a blast at a plant producing explosive materials in central Iran, local media reported, while three days later, a pipeline explosion at a petrochemical complex near Iran's Gulf coast left one dead.

Meanwhile, Iran views arch-rival Israel as the top suspect behind two incidents in the past year at its nuclear sites that Tehran has branded acts of sabotage.

Some in the Islamic republic see the various events as the result of attacks by Israeli agents, while others consider US sanctions -- which almost completely isolate Iran from the rest of the world, complicating the maintenance of industrial facilities -- as a more likely cause.