SEOUL, South Korea - South Korea's president said Saturday his country won't give in to North Korea's nuclear and missile threats, while Pyongyang accused Seoul of sending patrol boats into its territorial waters -- the scene of past bloody naval clashes.
In France, President Barack Obama suggested a new, stronger response to North Korean nuclear and missile testing, saying the North has tested the limits of patient diplomacy intended to persuade the reclusive communist country to accept international demands and end to its nuclear program.
The North's official Korean Central News Agency alleged the patrol boats were sailing into North Korean waters daily around the rivals' disputed western sea border. The Korean-language report warned that aggressors would be dealt "merciless punishment that will be beyond imagination."
The claim was rejected by Seoul, which two days ago alleged one of the North's patrol boats violated its sea border in the same area. The boat turned back without incident after a 50-minute standoff with the South's naval ships, the South Korean military said.
The disputed waters -- where deadly clashes occurred in 1999 and 2002 -- are a potential flash point for the rivals. Many fear a minor dispute could quickly escalate into a major confrontation, especially with tensions soaring after the North's May 25 nuclear blast and recent missile tests.
Earlier Saturday, South Korean President Lee Myung-bak delivered a stern warning to the North in a nationally televised Memorial Day speech honouring the country's war dead at Seoul's National Cemetery.
"I would like to make it clear that there will be no compromise against things that threaten our people and security," Lee said.
Lee's words echoed those of U.S. officials, who have also said the North's former tactics of using military threats to win much-needed food and energy aid would no longer work.
Obama, who was in France to commemorate the D-Day invasion, promised to take "a very hard look" at the next steps to take over North Korea's recent actions.
"Diplomacy has to involve the other side engaging in serious way, and we have not seen that reaction from North Korea," Obama said. "I don't think there should be an assumption that we will simply continue down a path in which North Korea is constantly destabilizing the region and we continue to act in the same ways."
Washington is considering punishing North Korea with its own financial sanctions, apart from whatever the UN might decide to adopt.
At the UN, lengthy closed-door negotiations about sanctions appeared to be close to an end. The measure was being worked out by five veto-wielding Security Council nations -- the U.S., China, Russia, Britain and France -- along with Japan and South Korea.
The seven nations have sent a draft of the measure to their capitals for comment, and ambassadors are expected to continue meeting early next week to discuss the governments' reactions.
The draft calls on UN members to immediately comply with sanctions imposed in 2006 after North Korea's first nuclear test, which include an arms embargo on heavy weapons, ship searches for illegal weapons and a ban on luxury goods.
South Korea's president also demanded the release of a South Korean worker detained in late March at a joint industrial complex in the northern border town of Kaesong. Pyongyang has denied Seoul access to the man -- accused of slandering the regime -- and his whereabouts were unclear.
Lee said, "North Korea should return our detained worker without condition."
Also held in the North were American TV journalists Laura Ling and Euna Lee, who worked for former Vice President Al Gore's California-based Current TV. They were arrested March 17 while reporting about the trafficking of women along the China-North Korea border. It's unclear if they strayed into the North or were grabbed by aggressive border guards who crossed into China.
The reporters' trial had been scheduled to begin Thursday, but there has been no confirmation that the proceedings have started.
In Washington on Friday, U.S. Secretary of State Hillary Rodham Clinton said, "I have met with their families and I've shared the grave anxiety that they feel about the safety and security of these two young women. We call again on the North Korean government to release them and enable them to come home as soon as possible."
