SEOUL: The United States and South Korea failed to revive a stalled free trade agreement on Thursday, dealing a blow to both countries' leaders and putting a brake on bilateral trade. US President Barack Obama and South Korea's Lee Myung-bak said negotiators would continue talks to address US concerns that the deal does not do enough to open South Korean markets to US beef and autos. “We agreed that more time is needed to resolve detailed issues and asked trade ministers to reach a mutually acceptable deal as soon as possible,” Lee told told a joint news conference with Obama on the sidelines of a G20 summit. The deal, if ratified by the two countries' assemblies, would be one of the largest free trade pacts ever. It is the largest signed by the United States since the North American Free Trade Agreement that went into effect in 1994. Studies said the deal would boost the $66.7 billion annual two-way trade by as much as a quarter. Lee said negotiators would return to the table after the G20 meetings are over this week to try to resolve US concerns but rejected the suggestion that trade between the two allies was on a fundamentally unfair footing. “US trade (deficit) against South Korea is about $8 billion a year. Americans seems to think it is very large; it may once used to have been, but it's come down by a lot,” Lee said, adding the two were on more or less an even playing field when US-made parts and intellectual property rights were factored in. Obama said he was confident the two sides would eventually reach an agreement and was reassured of Lee's commitment. “President Lee and I agreed that we need to make sure that over the next several weeks, we are crossing all the T's, dotting all the I's, being able to make the case to both the Korean people and the United States population that this is good for both countries. The two sides have been working frantically to address US congressional and industry demands for changes to the deal signed in 2007 by the countries' previous administrations. Two powerful US lawmakers from Michigan, the heart of the US auto industry, said in a joint statement further negotiations would succeed “only if South Korea adopts concrete steps to open its market to US exports.” Levin is chairman of the powerful House Ways and Means Committee.