MOSCOW, April 21 - The U.S. Justice Department's organized crime division is investigating RosUkrEnergo AG, a company that supplies Russian and Central Asian natural gas to Ukraine, Reuters reported citing diplomatic and financial sources.

Russian gas monopoly Gazprom owns half of RosUkrEnergo, whose opaque ownership structure has come under the spotlight at a time of growing fears in Europe over the security of energy supplies from Russia after Gazprom briefly cut supplies to Ukraine in January in a price dispute.