Moves by some oil producing countries to raise taxes imposed on international oil firms, or to change their contract terms could bring about unexpected impacts, Rodrigo Rato, head of the International Monetary Fund (IMF) said at a two-day OPEC seminar in Vienna.

    Rato called on OPEC member states to implement their policies on encouraging international energy firms to invest and sharing investment risks between the host countries and oil producers.

    Such oil producing countries as Venezuela, Bolivia, Chad, Algeria and Russia were adopting resources nationalism to seek more profit and control rights from multinational corporations, which drilled for energy in their oil and gas fields, the high-profile IMF official said.

    "This could backfire, as they create significant disincentives to new investment in oil production, thus ultimately affecting the governments' long-run revenues," Rato said.

    Rato also described a slowing U.S. housing market and possible oil supply disruptions as threats to the world economy.

    "Sudden or unexpected supply disruptions in the oil market - should they occur - could have more adverse effects than have occurred up to now," he said, adding that the impact of higher oil prices had been moderate so far, in large part because they had gone with strong demand for other commodities, goods and services.

    Rato said that domestic fuel prices in all countries should be set to reflect economic and social costs, and to promote a response to an appropriate demand.