Anglo-Australian mining giant Rio Tinto on Thursday reported record underlying first-half earnings of US$7.8 billion, a 35 percent increase on-year due to strong Asian demand for its commodities. Rio said it had been a \"record breaking\" period for the company, with first-half cash flow of $12.9 billion, a 31 percent premium on the previous corresponding period, and net profits of $7.587 billion. The results, which included record underlying earnings before tax and other factors of $14.3 billion -- 27 percent higher than first-half 2010 -- came in slightly below market expectations. The confident miner expanded its $5 billion share buyback programme to $7 billion in recognition of what chairman Jan du Plessis described as Rio\'s \"continued strong financial performance\". \"Conditions have remained favourable over the past six months due to strong Asian demand, although the volatile economic environment that we highlighted 18 months ago, continues to exist, driven by significant macro economic imbalances,\" said du Plessis. Chief executive Tom Albanese said volumes were lower in the half due to severe weather events in Australia but \"we were able to take advantage of higher prices for our products,\" to the tune of $4.997 billion. Currency movements, including the marked depreciation of the greenback against the Australian dollar, wiped $810 million off the bottom line, while higher oil prices cost $95 million. Rio\'s expansion of its flagship Pilbara iron ore project was now six months ahead of schedule and underlying earnings from the key sector jumped 45 percent in the half to $5.952 billion, despite cyclones and flooding hitting volumes. It flagged full-year iron ore production in excess of 240 million tonnes. Demand for coal was \"robust\" in the half, with India and China offsetting falls in the Japanese market, but Rio said the Australian summer\'s wild weather had driven steelmaking coal volumes down 20 percent on 2010 first half figures. Total energy group earnings, which also includes uranium, were 39 percent lower than the first half 2010. Rio forecast steelmaking coal production of eight million tonnes for the year and 18 million tonnes of thermal coal, burned to produce power. Albanese said the outlook for Rio was \"positive\" for the rest of the year and into 2012, with Chinese growth to expand by 9.5 percent, but warned of significant clouds on the horizon. \"There are important risks to this outlook related to the pace of credit tightening in developing countries and the threat of financial crises arising from sovereign debt problems in Europe and the United States which could destabilise commodity markets,\" he said. \"Our view remains that our markets will continue to experience higher than average growth but they will be characterised by elevated volatility and scope for discontinuities,\" added Albanese. Dual-listed Rio closed 1.3 percent lower at Aus$76.58 on the Australian stock exchange, which closed before the results were released.