An explosion struck an oil pipeline in Iran's oil-rich southwestern province of Khuzestan early Friday, triggering a blaze that took firefighters hours to put out, news agencies reported.
Abdohossein Rezaeizadeh, spokesman for the provinces' branch of the Iranian national oil company, told the official IRNA news agency that the causes of the blast and the subsequent fire were under investigation.
There were no immediate reports whether anyone was injured in the incident.
The semi-official Mehr news agency said the explosion happened at around 1:30 a.m near Susa, some 430 miles (700 kilometers) southwest of Tehran. The flames rose 130 feet (40 meters) up into the sky, the report said.
The pipeline feeds up to 4,000 barrels of oil a day to the nearby Ahvaz oil processing unit, some 62 miles (100 kilometers) south of the site of the explosion.
Iran's oil and gas sector has been hit by an increasing number of explosions recently but authorities rarely provide any explanation for them.
Most of the pipelines are decades old and encumbered with lack of maintenance and frequent technical failures. However, there have been occasional cases of sabotage, mostly reported in the northwest.
Last week, an explosion struck a major pipeline carrying gas to Turkey. The blast, which temporarily cut the gas flow, took place in morning hours near a border crossing but no one was injured. Authorities blamed it on Kurdish rebels operating in the area.
In April, three explosions hit gas pipelines near the holy city of Qom in central Iran, briefly cutting the flow of gas from Iran's gas refineries in the south to the country's northwest.
Similar explosions rocked the pipeline in the same area in February. Officials at the time said the blasts were not caused by technical failures but did not say if they were acts of sabotage.
Iran is OPEC's second largest oil exporter, and sits atop 137 billion barrels of conventional crude oil. It also holds the world's second largest natural gas reserves _ roughly 28 trillion cubic meters.
Some 80 percent of the country's foreign revenue comes from exporting crude.