The U.S. and South Korea declared that any North Korean aggression "is not to be tolerated," following two deadly incidents last year, and the South's defense minister cited a "very high" probability that the North will resume its provocations in 2012 as it marks the centennial of its founder's birth.
U.S. Defense Secretary Leon Panetta, speaking at a news conference with South Korean Defense Minister Kim Kwan-jin, said the allies are engaged in "counter-provocation" planning to reach agreement on how they would respond _ individually or jointly _ in the event of further North Korean aggression.
Tensions remain high on the Korean peninsula, largely stemming from the North's deadly bombardment of a front-line South Korean island that killed four people in November 2010. The South also holds the North culpable for the deaths of 46 sailors on a South Korean warship that sank in March 2010.
Kim promised that if the North engages in further provocation his country will make an initial response "in the form of self-defense," and that later there would be a "joint response using available assets."
Panetta did not say how the U.S. would join in a military response, but the U.S. has a treaty obligation to support the South in the event of North Korean aggression, whether by force or through other means.
There are about 28,500 U.S. troops in South Korea.
"We can provide strong and effective responses to those kinds of provocations if we work together and if we consult with each other and if we develop the kind of coordinated response that we think is necessary," Panetta said.
In a joint U.S.-South Korean statement, Panetta and Kim said they had decided to increase "combined watch activities" in advance of an international summit planned for Seoul next spring. They did not elaborate, but the statement appeared to mean they would boost intelligence gathering and surveillance.
The statement reaffirmed their solidarity and vigilance against a potential attack by the North. And Panetta reaffirmed, as a routine matter, that the U.S. nuclear umbrella extends to South Korea.
"The minister and the secretary urged North Korea to abandon all nuclear weapons and existing nuclear programs," they said, and urged the North to "demonstrate its genuine will" to give up its nuclear ambitions through "concrete actions."
"It's no secret that denuclearization means that they have to stop testing, they have to stop developing weapons, they have to stop enriching" uranium and allow international nuclear monitors to re-enter North Korea, Panetta told reporters.
U.S. and North Korean diplomats held talks this week in Geneva to explore a possible resumption of international negotiations over the North's nuclear program, but despite reports of modest progress there was no word on when additional discussions might be held.
On Thursday, Panetta expressed doubt that diplomacy will persuade North Korea to surrender its nuclear weapons and he raised the prospect of stalemate leading to "escalation and confrontation."
After daylong meetings Thursday with South Korea's government leaders, Panetta told reporters he was concerned by North Korea's pattern of deliberately shifting from periods of modest accommodation with the West to episodes of violent aggression, perhaps with no real intention of giving up its nuclear ambitions.
Asked whether he thinks a renewed effort by the Obama administration to explore a possible new round of international negotiations with North Korea will work, Panetta was blunt.
"We're not sure where those talks are headed at this point," he said, referring to the Geneva discussions, where there was no apparent breakthrough.
"For that reason, I guess the word `skepticism' would be in order," he said.
The Pentagon chief said he believes, nonetheless, that efforts at a diplomatic solution must go on.
"On the one hand, we have to engage," he said. "We have to try to seek the hope that ultimately they'll do the right thing and join the international family of nations. ... But I think we always have to be cautious that at the same time, they're going to continue to develop their nuclear capability."
In the same session with reporters, the commander of U.S. Forces Korea, Army Gen. J.D. Thurman, indicated that he suspects the North Koreans are determined to keep up the expansion of their nuclear capabilities.
"Based on what I have observed, they show a willingness to continue to develop and test capabilities that can be associated with their nuclear program," Thurman said. "This is something we've got to remain vigilant on."
Panetta's first visit to South Korea as defense secretary is part of a broader U.S. effort to shore up South Korea's confidence in a military alliance that has endured for six decades.
Panetta met Thursday with the South Korean defense and foreign affairs chiefs and paid a courtesy call on President Lee Myung-bak.
In parallel talks, the new chairman of the U.S. Joint Chiefs of Staff, Army Gen. Martin Dempsey, and top officers from the U.S. Pacific Command met with top South Korean military officers for an annual review of the U.S.-South Korean military alliance.
Panetta has called the North "reckless" and a "serious threat" to peace on the Korean peninsula, which exploded in war in 1950 and drew the U.S. and other nations into a three-year conflict against the North and China.
Panetta was asked by reporters what he thinks can be done to break a cycle of North Korean behavior in which it alternately makes gestures of accommodation to the West, followed by provocations.
"The cycle ultimately has to be broken," he said. "There is either going to be an accommodation where they decide to make the right decisions with regards to their future and join the international family of nations ... or, if they continue these provocations, then obviously that's going to lead to the possibility of escalation and confrontation."
Robert Burns can be reached on Twitter at http://twitter.com/robertburnsAP