US equity-index futures and European stocks slid, erasing earlier gains, amid growing concern the sovereign debt crisis is hurting French banks. The cost of protecting European corporate bonds from default climbed to the highest level since April 2009. Copper rose and the Swiss franc weakened against all 16 major peers. Standard and Poor\'s 500 Index futures dropped 1.6 per cent at 8.18am in New York, after rising as much as 2.2 per cent. The Stoxx Europe 600 Index was down 1.9 per cent. Societe Generale SA dropped 8.5 per cent, extending Wednesday\'s 15 per cent plunge. China\'s yuan strengthened beyond 6.4 per dollar for the first time in 17 years. Copper advanced 1.7 per cent. A rout in global equity markets since July 26 has erased $7.9 trillion (Dh29 trillion) in equity values and made stocks in Europe and the US the cheapest in about two-and-a-half years. Central bankers are trying to restore investor confidence, with the Federal Reserve pledging to keep interest rates near zero through at least mid-2013 to bolster US growth and the European Central Bank buying bonds every day this week to cap borrowing costs.