MOSCOW, September 16 (RIA Novosti) - Russia's investment in the troubled U.S. mortgage giants Fannie Mae and Freddie Mac is estimated at around $30 billion, the Audit Chamber chief said on Tuesday.

"According to the Finance Ministry's official position, investment in these bonds was significantly reduced and now stands at less than $30 billion," Sergei Stepashin said.

The U.S. government-sponsored firms, which together own or guarantee $5 trillion in U.S. mortgage debt, or almost 50% of the market, were taken over by a federal regulator last week in a bid to prevent their possible collapse amid a growing credit crisis.

Russia's Central Bank earlier said it held around $100 billion worth of bonds in Fannie Mae, Freddie Mac, and another mortgage firm, FHLB, which are guaranteed by the U.S. government, but has cut that by more than half since the firms' troubles became clear.

The first deputy chairman of Russia's Central Bank, Alexei Ulyukayev, said earlier that Russian investment in Fannie Mae and Freddie Mac bonds stood at some $50 billion as of late August. Another $10 billion was invested in FHLB.

Russian officials have repeatedly said the Russian market has remained unaffected by the global financial crisis, but independent economists argue that stability rests on the economy's dependence on exports on hydrocarbons, prices for which have remained relatively high so far.