"Today Gazprom completed the deal for the acquisition of 51 percent of SeverEnergia," the state-controlled gas giant said in a statement.
Gazprom put the size of the deal at 1.6 billion dollars (1.1 billion euros) and said the Italian firms would now own 49 percent of SeverEnergia, which had previously been 60-percent owned by ENI and 40-percent by Enel.
SeverEnergia holds licences for exploration and production of oil and gas in western Siberia.
The firm owns a number of assets that once belonged to Yukos, which was declared bankrupt and saw its assets auctioned off after the arrest of its billionaire owner Mikhail Khodorkovsky in 2003.
SeverEnergia, then known as Enineftegaz, bought the assets at a 2007 auction which was seen as the final stage of the dismemberment of Yukos, which was once Russia's largest oil producer.
The former Yukos assets included the Arcticgaz and Urengoil energy companies as well as a 20 percent stake in Gazprom's oil wing, Gazprom Neft.
In April, Gazprom agreed to pay ENI more than four billion dollars to buy back the 20 percent stake in Gazprom Neft, executing a buyback option that ENI granted Gazprom immediately after the 2007 auction.
Some analysts have said that Moscow hatched the buyback scheme in a bid to keep Yukos assets in state hands and that the Italian companies were brought into the controversial bankruptcy auction to lend it legitimacy.
Wednesday's deal means that Arcticgaz and Urengoil are now in Gazprom's hands too.
Italy has one of the closest relationships with Russia of any European country, and ENI has supported Gazprom's efforts to build the South Stream gas pipeline that would supply Russian gas to southeastern Europe.
Russia in recent years has re-asserted state control over many energy assets that were previously owned by wealthy industrialists like Khodorkovsky or foreign oil majors.
Many of Yukos' most valuable assets went to another state-owned company, Rosneft, which took over Yukos' crown as Russia's largest oil firm.
Khodorkovsky is currently serving an eight-year sentence for fraud and tax evasion and is now on trial again in Moscow on fresh charges of financial crimes that could see him land for two more decades in prison.
His supporters charge that he was jailed because of his opposition to then-president Vladimir Putin, but Russian officials insist he is guilty of massive crimes stemming from the controversial privatizations of the 1990s.Copyright © 2009 AFP. All rights reserved.