U.S. Army Gen. Curtis Scaparrotti, the commander of the joint U.S.-South Korea command, told the two presidents that his team "works together every day to make sure that we defend the Republic of Korea and that we deter North Korea."
After a private classified briefing, Obama was to address some of the 28,000 American service members stationed in South Korea. Following his remarks, Obama was to depart for Malaysia, the third stop on his four-country Asia swing.
During a morning meeting with a dozen corporate executives, Obama said the U.S. and South Korea are going to have "one of the key economic relationships of the 21st century." The executives represented businesses including Hyundai, Samsung, Korean Air, Microsoft, Boeing, Goldman Sachs and others.
"As important as the security relationship is and the alliance is between the Republic of Korea and the United States, what is also important is the incredible and growing economic ties that are creating jobs and opportunity in both countries," Obama said.
While in Seoul, Obama has also paid tribute to victims from last week's ferry disaster. The vast majority of the 300 dead or missing were students from a single high school near the capital city.
The president also has had to attend to the ongoing crisis in Ukraine, as a fragile accord with Russia aimed at stemming tensions appears to have crumbled. Obama spoke by telephone with European leaders to discuss the possibility of deepening economic sanctions on Russia, though it appeared unlikely that new penalties would be imposed on Friday.
Despite the distractions of other issues, the president's core mission in Seoul is to underscore the U.S. commitment to the security of South Korea and other allies during a period of uncertainty in the region. While the U.S. has long been the most powerful military influence in the Asia-Pacific region, Pentagon spending is being slashed at the same time China has been boosting its defense budget.
Beijing still lags far behind the U.S. in both military funding and technology. But its spending boom is attracting new scrutiny at a time of severe cuts in U.S. defense budgets that have some questioning Washington's commitments to its Asian allies, including some who have lingering disputes with China.
At the same time, the U.S. military is seeking to redirect resources to the Asia-Pacific as it draws down its commitment in Afghanistan, though there is concern that budget cuts could threaten plans to base 60 percent of U.S. naval assets in the region. Chief of Naval Operations Adm. Jonathan Greenert recently warned that U.S. capabilities to project power "would not stay ahead" of potential adversaries, given the fiscal restraints.
The U.S. military continues to have a robust presence in South Korea, in part to serve as a deterrent to the North. Obama on Friday declared the alliance between the U.S. and South Korea "a linchpin of security in Asia."
"Our solidarity is bolstered by the courage of our service members, both Korean and American, who safeguard this nation," Obama said during a news conference Friday with Park, the South Korean president.
Ahead of his meetings with Park, Obama paid tribute to U.S. soldiers killed in the Korean War. He placed a wreath beside a plaque bearing the names of some of those killed as a bugler played out taps.
Obama will speak Saturday at Yongsan Garrison, headquarters for U.S. forces in South Korea. Before his remarks, Obama and Park will have a rare joint leaders briefing with the commander of the U.S-South Korea Combined Forces Command.
Both countries are closely watching North Korea, which has threatened to conduct its fourth nuclear test. Obama and Park both warned Friday that the launch could lead to tougher sanctions, with Park also declaring that it could trigger an undesirable nuclear arms race in the region and render further nuclear negotiations pointless.
The website 38 North, which closely monitors North Korea, said commercial satellite imagery from Wednesday showed increased movement of vehicles and materials near what are believed to be the entrances to two completed tunnels at Punggye-ri nuclear test site. The movements could be preparations for an underground atomic explosion, although predicting underground tests is notoriously difficult.