The secretive activities of multibillion-dollar sovereign investment funds being set up by reserve-rich nations are a source of growing concern, the International Monetary Fund (IMF) said yesterday.

Simon Johnson, the IMF’s chief economist, said that the organisation was growing increasingly uneasy over the role of these sovereign funds, which have been burgeoning in scale and have eclipsed the hedge fund sector to control an estimated $2.5 trillion (£1,250 billion) of global wealth.

Mr Johnson’s comments in Frankfurt come amid rising anxiety over sovereign funds, which has been fuelled after their introduction by both Russia and China. Morgan Stanley, the investment bank, estimates that sovereign investment funds, which draw on slices of capital-rich governments’ foreign exchange reserves and export earnings, could reach about $12 trillion in value by 2015.

Kuwait, Alaska and the United Arab Emirates set up such investment funds to manage state resources efficiently years ago to help to offset periods of low oil export earnings when crude prices fall, providing a financial cushion for their public finances.

Norway is also noted for running an investment fund, drawing on its oil earnings to provide a financial asset for future generations – a model that Russia now mimics.

Mr Johnson said that the IMF was worried that as the number and scale of sovereign investment bodies has risen around the world, so had their potential impact, when little was disclosed about their activities. The majority of such funds are highly secretive about their investments.

“There are an increasing amount of financial flows going through black boxes. Hedge funds are black boxes. Sovereign wealth funds are black boxes. We don’t know what happens and we should worry about that,” Mr Johnson said. “Black boxes should make us uneasy . . . People are beginning to feel uncomfortable about this.”

He added that the IMF’s efforts to understand the potential financial risks from sovereign funds remained at a “pretty early stage”. Key concerns were the amount of leverage that funds might employ.

Mr Johnson also echoed a warning this week from the Basle-based Bank for International Settlements over a growing threat from global inflationary pressures. He said that the world economy was set to power ahead, with annual growth of about 5 per cent. “There are real inflationary pressures when you run a world economy this fast,” he said.

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