GYEONGJU, South Korea (AFP) - The United States urged G20 nations to reform their currency regimes to shore up the fragile world economy after a devastating crisis, but faced resistance to its ideas Friday. G20 finance ministers and central bankers opened a two-day meeting in South Korea, stalked by warnings of an all-out currency war between debtor nations such as the United States and export powerhouses such as China. The G20 meeting, and parallel talks among the G7 grouping of North America, Western Europe and Japan, faced warnings that the world was at risk of relapsing into 1930s-style trade protectionism. South Korean Finance Minister Yoon Jeung-Hyun urged his G20 guests to exploit their collective heft on currency disputes, IMF reform and ensuring mega-banks cannot imperil the world economy two years after the crisis erupted. History demanded that the G20 build a new post-crisis international economic order, he told the meeting, looking ahead to a November 11-12 summit in Seoul of leaders including the US and Chinese presidents. Canadian Finance Minister Jim Flaherty, following talks with Chinese counterpart Xie Xuren, told reporters theres a willingness (by Beijing) to open the door to more flexibility over time. I think theres a recognition that this currency issue has to be addressed. If its not, then we know from history the path that we end up going down, which is not good for any of us, Flaherty said. In a letter to his G20 colleagues, US Treasury Secretary Timothy Geithner urged nations running big trade surpluses to change their exchange-rate policies. He did not name the nations but China seemed the clear target. He suggested that countries should aim to reduce surpluses or deficits to a targeted share of gross domestic product in the coming years. Officials said the target would be four percent of GDP by 2015. Chinas current account surplus stood at 4.9 percent of GDP in the first half, and targeting the surplus would be an indirect way for Washington to cajole Beijing into letting its currency appreciate. But other major exporters such as Germany would also be affected by the Geithner plan, and are already unhappy at being asked to remedy failings in the global financial system that were exposed by a US-generated crisis. There was no immediate reaction from China on Friday, but Japanese Finance Minister Yoshihiko Noda said Geithners plan to focus on the current account was not realistic, expressing opposition to strict, numerical targets. Germany has also expressed doubts about the plan. Australian Treasurer Wayne Swan expressed wariness about a one-size-fits-all approach. Canadas Flaherty said Geithners idea was helpful but added: Different countries view that in different ways. G20 nations with large deficits should boost national savings via credible medium-term fiscal targets and boost their exports, Geithner said in the letter. Conversely, G20 countries with persistent surpluses should undertake structural, fiscal and exchange-rate policies to boost domestic sources of growth and support global demand, he wrote. With a super-loose US monetary policy weakening the dollar, G20 economies such as Japan, South Korea, Brazil and Indonesia have intervened in recent weeks to curb an alarming rise in their currencies. But for the United States, which is in the throes of election season, China lies at the root of the problem owing to its firm control over the yuans value. Critics say that policy gives Chinas export machine an unfair edge. Apparently signalling they want a temporary truce, the G20 ministers will pledge to refrain from competitive undervaluation of their currencies, according to a draft statement obtained by Dow Jones Newswires. They will move towards (a) more market-determined exchange rate system, the draft said, without spelling out how. China this week surprised markets by raising interest rates to rein in accelerating inflation. But it has shown no appetite for coordinated action to unshackle the yuan, for fear of driving many of its exporters out of business. After a volatile day on Asian currency markets, RBC Capital Markets said a grand plan to deal with global imbalances looks set to remain elusive.