SEOUL, May 24, 2010  -- Days after North Korea threatened an all-out-war against South Korea, President Obama ordered the U.S. military to work with South Korea to "ensure readiness" and prepare for future aggressions.

"We endorse President Lee's demand that North Korea immediately apologize and punish those responsible for the attack and, most importantly, stop its belligerent and threatening behavior," the White House said.

South Korean President Lee Myung-bak said today that North Korea would have to "pay a price" for the torpedo attack on a South Korean navy ship in March that killed 46 young sailors.

But even as the two Koreas exchanged fierce rhetoric, analysts in Seoul said a military response is unlikely.

"It's a repeated cycle in which relations have had its ups and downs in the past 60 years," said Koh Yu-Hwan, professor of North Korean studies at Dongguk University. "Today, the worst hit the peak, and now the only direction is for each sides to back down and cool off."

Officials in South Korea, the United States and Japan want to bring the issue before the United Nations Security Council and impose stronger and tighter sanctions, at least as a symbolic gesture because the North Korean economy has already hit rock bottom.

But China remains reluctant to join in on the international condemnation. "China has a complicated long-term tie with North Korea, not just politically but ideologically and with legal commitment," said Jin Canrong, associate dean at the School of International Studies at Renmin University of China, referring to the 1961 China-North Korea Treaty on Friendship, Cooperation and Mutual Assistance.

Some analysts said China simply does not want a war on its doorstep and millions of refugees pouring in across its border.

Secretary of State Hillary Clinton has made efforts to persuade Chinese officials support condemnation during the two-day annual U.S.-China high level talks in Beijing. She told reporters that they were "in the midst of very intensive consultations" and "the Chinese recognize the gravity of the situation we face."

China Unwilling to Condemn North Korea

Clinton said both countries are "working hard to avoid an escalation, belligerence and provocation," but "at the same time to send a message to North Korea that we are not simply resuming business as usual."

But Chinese President Hu Jintao stopped short of supporting international condemnation saying the two nations should together "manage regional hotspots" and "safeguard world peace and security," without mentioning North Korea by name.

His South Korean counterpart addressed North Korea with unusually tough rhetoric, unprecedented in recent decades when a push for reconciliation and peace took hold.

In a nationally televised address, Lee demanded immediate apology saying South Korea had "tolerated and tolerated" but "from now on, we will not tolerate anymore provocative acts by the North."

He suspended ongoing inter-Korean trade, investment, and aid but exempted humanitarian aid for North Korean children and production at the jointly run Kaesong Industrial Complex north of the border.

He also banned North Korean merchant ships from passing South Korean waters. "If our territorial waters, airspace or territory are violated, we will immediately exercise our right of self-defense," he vowed.

But North Korea experts in Seoul noted that the warnings did not intend to corner Pyongyang for good. The address intentionally left room for future concessions by not specifically naming North Korean leader Kim Jong-Il in the statement.

"If we pointed the finger directly at Kim Jong-Il, that would have been a point of no return because from their point of view, that is non-negotiable," professor Koh said.

Now, analysts said, there is still room for North Korea to take a step back by blaming the torpedo attack on its overzealous naval forces and say they actually shot the South Korean submarine without specific endorsement from Pyongyang.

ABC News' Clarissa Ward and Laura Greene contributed to the reporting of this story from Beijing and Washington D.C.