US Treasury Secretary Timothy Geithner's proposals, outlined in a letter to the Group of 20 major developed and emerging nations, met with immediate resistance on the opening day of a two-day meeting of top finance officials.

Japan's Finance Minister Yoshihiko Noda on Friday called the idea of targets "unrealistic." The gathering of G20 finance ministers and central bank governors in the South Korean city of Gyeongju comes just two weeks after their meeting in Washington failed to iron out currency differences that have led to fears of a trade war that could trigger another economic downturn.

In such a scenario, countries devalue their currencies to gain a competitive advantage in a world economy that has yet to fully recover from the global financial meltdown two years ago. Trade barriers are erected in response, hitting international commerce and reversing the economic recovery.

Nations in Asia and other regions have been trying to stem strength in their currencies amid sustained weakness in the US dollar out of fear their exports will become less competitive in world markets. At the same time, China's currency has been effectively pegged to the dollar, provoking an outcry that it is being kept artificially low and giving China's exporters an unfair advantage.

According to officials at the summit, Geithner's idea is to establish numerical targets for current account balances, be they surpluses or deficits — aiming to reduce conflicts over exchange rates by allowing the currencies of trade surplus countries to rise in concert. The current account is a broad measure of a country's total trade and investment with the outside world.

Striving to meet such targets could over time limit Asia's vast trade surplus with most advanced economies but it's uncertain whether specific goals will garner broad support within the G20.

Asia becoming less reliant on exports for growth is seen as one of the adjustments the world economy should make in the wake of last year's recession to ensure more stability in the global economy and markets. Stronger currencies, meanwhile, would make imported goods cheaper and boost local spending as a contributor to economic growth.

Canadian Finance Minister Jim Flaherty said the currency issue must be addressed and that no one in the G20 wants to end the meeting without an action plan.

Flaherty said he supported Geithner's ideas in the letter, which was written to G20 member nations ahead of the meeting. He said the letter also urges the group to refrain from competitive currency manipulation.

South Korean President Lee Myung-bak, chair of the upcoming G20 leaders summit, hinted at the challenges facing members as they delved into discussions. Countries have diverse economic situations so they may turn to different policy strategies on current accounts and foreign exchange, he said. But nations "must find a way for a mutual win-win," Lee said.

China, the world's No. 2 economy, is under renewed pressure over its management of the yuan. Flaherty said he met with his Chinese counterpart Xie Xuren on Friday. "I think there's a willingness to open the door to more flexibility over time," he said of Beijing.

The broad weakening of the dollar and the outlook for possible further monetary easing by the Federal Reserve is another factor adding to the strain over currencies.