Britain\'s biggest insurer Prudential announced on Monday a plunge in half-year net profit but said its operating performance improved thanks to a strong showing in the United States and Asia. Profit after tax tumbled 59 percent to £365 million ($565 million, 424 million euros) in the six months to the end of June compared with the first half of 2012, Prudential said in an earnings statement. The company said earnings were hit by short-term fluctuations in investment returns. Group operating profit, based on longer-term investment return assumptions, jumped 22 percent to £1.415 billion in the first half of 2013. \"The global economic environment remains uncertain, with continued equity market and interest-rate volatility often driven by short-term news flows, as confidence is still fragile,\" Prudential chief executive Tidjane Thiam noted in the statement. \"Despite this, the long-term structural trends of a growing middle class, low insurance penetration and faster relative economic growth underpin our profitable growth in south-east Asia. \"The transition of US \'baby-boomers\' into retirement and the ageing of the UK population provide us with additional opportunities to generate significant value,\" Thiam added. Prudential\'s share price was up 3.55 percent at 1,226 pence in reaction to the group\'s operating performance. London\'s benchmark FTSE 100 index was down 0.25 percent overall.