March 21 (Reuters) - Rusoro Mining Ltd, backed by Russia's Agapov family, said on Thursday it had filed a statement of claim against the Venezuela state and is seeking $3.03 billion in compensation over the nationalization of its gold assets in the South American country.

The claim was filed at the World Bank's International Center for Settlement of Investment Disputes, or ICSID, under the provisions of Canada-Venezuela bilateral investment treaty.

The Venezuelan government already faces about 20 cases at the tribunal, including multibillion-dollar claims by U.S. oil companies Exxon Mobil Corp and ConocoPhillips.

Late President Hugo Chavez set his sights on the gold industry after quarreling with Rusoro and other foreign companies, which complained that limits on exports were hurting their efforts to develop projects in the South American country.

A new law came in force in 2011 aimed at "overturning the serious impact of the capitalist mining model" by banning all exports and giving the Venezuelan state at least 55 percent of joint ventures.

It also fixed the royalty rate for most projects at 13 percent, which foreign miners said would scare away any investors who were still deciding whether to work in Venezuela.

Vancouver-listed Rusoro was the largest gold miner operating in Venezuela and had enjoyed good relations with Chavez's government. It produced nearly 150,000 ounces in Venezuela in 2010, and about 80,000 ounces last year before the new rules took effect.

"The filing of the Statement of Claim represents a significant milestone in the arbitration process and we firmly believe in our case and the pursuit of fair-value compensation for the loss of our significant investment in Venezuela," Chief Executive Andre Agapov said in a statement.