The United States and its ally South Korea are "running amuck with bloodshot eyes to find a pretext for a war of aggression," North Korea's official news agency said Tuesday. It warned that the North's people are prepared to sacrifice their lives to defend "Korean-style socialism … which is (the) most advantageous in the world."

U.S. presidents have dealt for decades with similarly bellicose threats when traveling to Seoul, where Obama arrived Wednesday in the latest stop on his Asian tour.

The challenge for Obama will be to succeed where his predecessors failed by getting North Korea to give up its nuclear program for good — a task that will require the help of South Korea.

Tensions in the region are high after the biggest naval clash in seven years between the North and South, which have technically been at war since the 1950s.

North Korean dictator Kim Jong Il has frustrated the world during the past year with on-again, off-again concessions on the nuclear issue.

Most recently, Kim's regime has refused to return to negotiations unless they take place directly with U.S. officials.

Yoon Dae Kyu, a professor at Kyungnam University in Seoul, says he expects no immediate breakthroughs on Obama's trip but is optimistic the president can help lay the groundwork for progress in coming months.

He said aggressive rhetoric such as the recent report by the North's Korean Central News Agency may indicate a growing desperation there amid food shortages and uncertainty over the aging Kim's future.

"Time is not on the North Koreans' side," and they will have fewer and fewer alternatives going forward, Yoon said. He dismissed the threats, saying, "They cannot feed their people at this moment, so how could they attack South Korea?"

There is also a better chance of a united negotiating front against the North. South Korean President Lee Myung Bak, with whom Obama met with today, is more pro-U.S. than his predecessor.

After their meeting, Obama and Lee signaled impatience with North Korea, declaring fresh, united steps to get that nation to give up its nuclear weapons, the Associated Press reported.

Lee said Obama had rallied behind his idea for a one-time "grand bargain" with the North of aid and concessions in exchange for de-nuclearization, rather than the stalled step-by-step process. And Obama said his envoy would travel to North Korea early next month for the first bilateral talks with the communist government since he took office.

Jin Linbo, a Korea specialist at the China Institute of International Studies in Beijing, warned that progress will be difficult without more cooperation from China, which is North Korea's main ally and economic sponsor.

Jin said that is unlikely for now. A day after welcoming Obama to Beijing, Chinese Vice President Xi Jinping welcomed a top North Korean general to the city Tuesday.

"In the end, only North Korea can decide to give up its nuclear weapons program," Jin said. "Obama is visiting South, not North Korea."

Other issues on the agenda include trade. A free-trade agreement between South Korea and the United States was signed in 2007 under previous leaders but has been stuck in Congress ever since. Obama has expressed concerns about access to the South Korean market for U.S. auto exports.

Enlarge Pool photo President Obama arrives at a U.S. Military Airbase on Wednesday in Osan, South Korea. Obama is in South Korea for two days as the final desitination of his Asia tour.