UPDATE 1-Gazprom to exercise ENI buyback option early April

* Gazprom to buy back 20 pct of Gazprom Neft -industry sources

* Gazprom will also buy back Russian gas assets

* Exercising option could cost $5.5 billion, talks ongoing (Adds background on buyback option)

MOSCOW, March 25 (Reuters) - Russia's Gazprom GAZP.MM plans to exercise an option to buy back 20 percent of its oil arm Gazprom Neft SIBN.MM and Russian gas assets from Italy's ENI ENI.MI in early April, industry sources told Reuters.

“It’s going to be part of (Italian Prime Minister Silvio) Berlusconi’s visit to Moscow,” one of the sources said on Wednesday.

Industry sources added that Gazprom was currently talking to a number of Russian state banks to raise financing to exercise the option, which could cost up to $5.5 billion.

However, the sources said the two sides have yet to reach an agreement on the final price.

ENI acquired the stake in Gazprom Neft at a state auction of bankrupt oil firm YUKOS in April 2007 and immediately agreed to sell the stake to Gazprom within two years.

Gazprom, Russia’s gas export monopoly, currently owns 75 percent of Gazprom Neft. (Reporting by Dmitry Zhdannikov; Editing by Michael Urquhart)