Rosneft buys into gas producer Itera to challenge Gazprom

* Rosneft buys 6 percent of Itera

* Move in line with plan to strengthen foothold in gas mkt

* Rosneft gives no financial details

MOSCOW, July 20 (Reuters) - Russia's top crude producer Rosneft has acquired 6 percent of mid-sized natural gas company Itera, in line with its plans to strengthen its foothold in the gas market.

Rosneft gave no financial details when it announced the deal on Friday.

Rosneft, which accounts for almost a quarter of Russia's crude production, has long been eyeing expansion into the gas market dominated by another state-owned group Gazprom.

In 2011 Rosneft produced almost 12 billion cubic metres of gas (bcm), or less than 2 percent of Russia's total gas output.

In February, Rosneft announced a plans to team up with privately-owned Itera to jointly tap gas fields. It later filed a request to an anti-monopoly watchdog to acquire a stake of up to 51 percent in the gas producer.

Itera, which produces over 20 bcm of gas a year, was the monopoly trader of Turkmen gas via Russia to Ukraine in the 1990s. It lost its exclusive rights several years ago after a management shake-up at Gazprom and has failed to regain its position since then.

Last year, Russia's third-largest oil producer TNK-BP failed to secure a deal to acquire 50 percent in Itera, according to industry sources. (Reporting by Vladimir Soldatkin; Editing by David Holmes)