Enlarge By Charles Dharapak, AP President Obama meets with President Lee Myung-bak of South Korea on the sidelines of the G20 summit in Toronto, Saturday. TORONTO (AP)  President Barack Obama said Saturday that North Korea must be "held to account" for its alleged sinking of a South Korean warship, a tough statement of support for an ally and made at its leader's side. After talks with South Korean President Lee Myung-Bak on the sidelines of global summits here, the U.S. president used some of his strongest language yet about the March sinking of the South Korean warship Cheonan. An independent report has found that the ship's sinking was caused by a North Korean torpedo. "There has to be consequences for such irresponsible behavior," Obama said. South Korea has already referred the ship sinking to the U.N. Security Council, which could adopt a resolution condemning the North for the sinking or issue a less stringent presidential statement. Lee said he wants a "strongly worded" resolution. "We will do all that we can to deter any acts of North Korean aggression leveled against us," said the South Korean leader. Said Obama: "We stand foursquare behind him." Also pleasing Lee, Obama announced that he would submit to Congress early next year a long-upheld free trade agreement with South Korea. He said the U.S. will resume talks with South Korea to resolve issues that have blocked the accord. Those discussions will take place between now and the Group of 20 international summit, to be held in Seoul in November. Obama said he would present the accord to Congress within a few months after that. "It is the right thing to do," Obama said. The administration of George W. Bush negotiated a free trade deal with South Korea in 2007, but the agreement has been stalled in the United States since that time because of determined opposition led by U.S. automakers who contend that the agreement did not go far enough to remove barriers to the sale of U.S. cars in Korea. Since taking office in January 2009, the Obama administration, in the face of stiff opposition from U.S. labor groups, has refused to send the agreement to Congress for a vote. The tough talk toward North Korea by Obama and Lee was sure to be a topic in the U.S. president's next meeting, with Chinese President Hu Jintao. Since China is a veto-wielding member of the Security Council, its support is required for any resolution. But Beijing, as North Korea's main ally, has resisted punishment for Pyongyang. Obama also said that he and Lee had agreed, at South Korea's request and in light of the ship sinking, to delay handing off wartime operational control of Korean forces on the Korean Peninsula from the U.S. to Korea until the second half of 2015. This gives "appropriate time ... to do this right," Obama said. Korea was to have assumed control of its own forces in 2012 in the event of war. Obama began his day by concluding a summit of the leading eight industrial democracies at a resort in Canada's forested Muskoka lakes region, then flew here for a second, expanded summit of the so-called Group of 20 nations. Those larger meetings, mostly being held on Sunday, were getting underway with a dinner. In between, Obama was meeting on the sidelines with important foreign counterparts. Copyright 2010 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed. Guidelines: You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. You share in the USA TODAY community, so please keep your comments smart and civil. Don't attack other readers personally, and keep your language decent. Use the "Report Abuse" button to make a difference. Read more