The International Energy Agency has trimmed its world economic growth forecasts for this year and next year, citing a weaker outlook for China and the United States. An \"exceptionally challenging macroeconomic backdrop\" over the past two months had forced the IEA to cut its estimates, it said, to 3.3 percent this year from the previous 3.5 percent. In terms of oil demand, the IEA left its 2012 growth forecast at around 800,000 barrels per day (bpd) to around 89.9 million bpd, with 2013 gaining a \"relatively muted\" 1.0 mbd to 90.9 mbpd, led by Asia. Prices are expected to fall a further 7.0 percent next year, which should marginally support demand, it added. For 2013, the global economy should grow 3.8 percent, down from a 4.1-percent estimate based on April figures from the International Monetary Fund, the IEA said. \"Concerns are mounting on the sustainability of the eurozone, there has been a definite easing in China\'s economic impetus and the US outlook has weakened,\" the International Energy Agency said in its latest monthly report. \"Ongoing debt concerns across the developed world will likely see associated austerity measures curtailing government, business and consumer expenditure levels alike,\" it said. The IMF is expected to issue new economic growth forecasts shortly. The IEA is a branch of the Organisation for Economic Cooperation and Development which also produces closely watched growth forecasts.