The Tuesday morning fire in one of Iraq's most important cities left the 140,000 barrels of oil per day refinery with "no damage," according to officials quoted by Argus media. It also reported an Oil Ministry official said a U.S. helicopter was near the refinery when it caught on fire.

Four workers were injured, Voice of America reports, which also sources an Oil Ministry official saying the helicopter started the fire.

Iran's Press TV reports the fire took place in the gas production unit of the Shuaiba refinery, the largest refinery in the south that local consumers rely on for fuel.

Basra sits on or near about 80 percent of Iraq's 115 billion barrels of proven reserves and is the key route for most of Iraq's oil exports.

Iraq's largest refinery, in Baiji, was set ablaze last week. The 300,000 barrels per day refinery is running again, the ministry said. An explosion at the liquefied petroleum gas unit started the fire, and it's not clear whether it has been repaired.