Four persons have been killed in a fire in Rag Sefid oil field in Iranian province of Bushehr, the media reported.The fire, which broke out on Sunday, was very huge and Iran's Red Crescent Society dispatched helicopters to extinguish it, Xinhua reported citing IRNA news agency. According to some reports, the cause of the accident was the eruption of gas from the oil field.Rag Sefid is located in Bushehr province, 950 km from Tehran.On Friday, six persons were killed and two injured after a fire erupted in Tehran Refinery. The leak of flammable materials was cited as the cause of the accident.