North Korea (search), which relies on outside aid to feed its people, marked the 63rd birthday of leader Kim Jong Il on Wednesday with feasts of pheasant and venison for the capital's elite amid heightened tension on the Korean peninsula over the communist state's nuclear weapons program.

But South Korea (search), dampening the North's festive mood, said there will be no large-scale economic cooperation until the dispute over the communist North's nuclear weapons programs is resolved.

North Korea flouted the international community last week by claiming it had nuclear weapons and was staying away from international nuclear talks where China, Japan, Russia, South Korea and the United States have urged it to abandon its atomic weapons development.

The announcement was a key theme in North Korea's celebration of Kim's birthday this year, with its media claiming that last week's "bombshell" declaration demonstrated Kim's "incomparable courage." Kim turned 63 Wednesday.

"The Americans swagger like a tiger around the world, but they whimper before our Republic as the tiger does before the porcupine," Pyongyang (search) Radio said. "That's because we have our Great Leader Kim Jong Il (search), who is undefeatable." The dispatch was alluding to a popular North Korean folk tale and TV animation where a porcupine defeats a tiger by sticking its quills in the tiger's nose.

To the outside world, the North's maneuver further isolated the impoverished country. North Korea has refused to rejoin the six-nation negotiations until Washington abandons what Pyongyang called a "hostile" policy.

"North Korea must return to six-party talks as soon as possible," South Korean President Roh Moo-hyun told a meeting of his top security ministers Wednesday. "If North Korea has anything to allege, it should make the allegations at the negotiating table."

South Korean Foreign Minister Ban Ki-moon said he told U.S. officials during a weeklong trip to Washington that his country has no plans to begin large-scale economic cooperation with the North before it agrees to end the nuclear dispute. Still, Ban said, South Korea would continue to provide humanitarian aid to the poverty-stricken state.

In the run-up to Wednesday's birthday, North Korea has escalated anti-American rhetoric and urged its people to rally around Kim.

"No matter how wild the U.S. imperialists may run, our country remains unfazed and the spirit of our army and people is sky-high," the North's main Rodong Shinmun daily said in a Wednesday editorial for the birthday, celebrated in the country as a national holiday.

In the capital Pyongyang, state-run TV displayed the usually quiet streets lined with banners wishing "good health and long life for the general," as Kim is commonly referred to as commander of the country's armed forces. Large crowds in colorful clothes or soldiers in uniform were shown dancing in Pyongyang squares.

Media reported the unseasonable blossoms of wild flowers, citing them as divine evidence that nature was also celebrating the birthday, the "common holiday of the humankind." Around the country, exhibitions were held featuring Kimjongilia -- a red flower cultivated to blossom around Kim's birthday.

Kim's Stalinist regime gave its elite feasts of pheasant and venison, according to North Korea's state-run Central TV, which was monitored by the South Korean news agency Yonhap.

Such feasts are a sharp contrast in a country that relies on outside aid to feed its people after suffering natural disasters that began devastating its economy in the mid-1990s.

There were reports last year that some of Kim's portraits had been removed from public buildings, suggesting possible cracks in his hold on power, but South Korean officials have insisted the North's government is nowhere near collapse and warned that such talk could push Pyongyang to desperate moves.