In a Veterans Day ceremony at a U.S. Army garrison in Seoul, South Korea, President Obama on Thursday honored those who fought in the Korean War and tied their legacy to the current standoff on the Korean peninsula, issuing a stern reminder to Pyongyang that the American military stood ready to defend South Korea from acts of aggression.

Speaking at an American outpost little more than 30 miles from the Demilitarized Zone, Obama said that the alliance between the United States and South Korea "has never been stronger."

"And along with the rest of the world, we've made it clear that the North Korea's pursuit of nuclear weapons will only lead to more isolation and less security for them," Obama said.

Echoing the kind of language employed by his predecessors -- including former President George W. Bush -- Obama said that the differences between North and South Korea provided the most vivid example in the world today between a free and thriving society and a closed and tyrannical one.

"It's a contrast that's so stark you can see it from space, as the brilliant lights of Seoul give way to the utter darkness of the North," Obama said. "This is not an accident of history. This is a direct result of the path that's been taken by North Korea -- a path of confrontation and provocation -- one that includes the pursuit of nuclear weapons and the attack on the Cheonan last March."

Obama was referencing the sinking of a South Korean warship off the Korean peninsula, which killed 46 South Korean sailors. An international report conducted by parties including South Korea and the U.S. concluded that a North Korean torpedo sunk the Cheonan -- a charge that North Korea has denied.

"In the wake of this aggression, Pyongyang should not be mistaken," Obama said. "The United States will never waver in our commitment to the security of the Republic of Korea. We will not waver."

Obama's firm rhetoric on North Korea was softened a bit when he added that "another path" was available for the isolated Communist regime if it lived up to its international obligations, leading to "a future of greater security and greater respect -- a future that includes the prosperity and opportunity available to citizens on this end of the Korean Peninsula."

Obama singled out U.S. servicemen and women from the Army, Navy, and Marines who were on hand at the ceremony for continuing to defend the security of South Korea and said they were following in the footsteps of what their predecessors fought to achieve 60 years ago.

"Because the Korean War ended where it began geographically, some ended up using the phrase ‘Die for a Tie' to describe the sacrifices of those who fought here," Obama said. "But as we look around in this thriving democracy and its grateful, hopeful citizens, one thing is clear: This was no tie. This was victory."

After delivering his remarks, Obama met with South Korean President Lee Myung-Bak. Appearing at a joint press conference with the South Korean leader, Obama said that the six-party talks, which were first launched in 2003 to address North Korea's nuclear program, had degenerated in 2005 when they became "talk for the sake of talking." Obama did not appear eager to restart the talks under the current circumstances.

"President Lee and I have discussed this extensively and our belief is that there will be an appropriate time and place to re-enter into six-party talks," Obama said. "But we have to see a seriousness of purpose by the North Koreans in order to spend the extraordinary time and energy that's involved in these talks. We're not interested in just going through the motions with the same result."

Before meetings began for the G-20 Summit on Thursday night, Lee made the unexpected announcement that South Korea and the U.S. had been unable to hammer out details of a new bilateral free trade agreement.

"President Obama and I agreed that we will give my trade minister and the U.S. Trade Representative more time so that they can finalize the technical issues," Lee said, adding later that he thought the future discussions "won't take too long."

Later on Thursday, Obama met with Chinese President Hu Jintao and said that the U.S.-China relationship had "become stronger over the last several years."

"We have created a structure -- a Strategic and Economic Dialogue -- in which our teams have been working on a whole range of issues," Obama said. "And we're seeing significant progress."