Tension is building as Pyongyang escalates its threats of attack against South Korea. The latest among them is a warning that North Korea would regard it as a “declaration of war” if the forthcoming Seoul nuclear security summit adopts a statement condemning its nuclear program.

Those remarks were contained in a statement carried by the North’s state-run news agency on Wednesday. It added: “If there is any provocative act such as the issuance of a so-called statement concerning ‘the North’s nuclear issue’ at the Seoul conference, it would constitute an extreme insult to the North’s deceased leaders who left denuclearization as their final wish.”

The intimidation followed the pinpointing two weeks ago of the Blue House and some areas in Seoul as the potential targets of shelling. Meanwhile, the North Korean media continued to vilify President Lee Myung-bak, the minister of defense and other Cabinet members, calling them turncoats for the entire Korean people.

Behind the saber-rattling is the North Korean military, which South Korean policymakers believe maintains the upper hand on foreign policy during the transition period after Kim Jong-il’s death in December. They believe Kim Jong-un, the untested young man who inherited power from his deceased father, has yet to put the military under his firm control.

While the North intensifies its verbal attacks, Kim Jung-un has been touring military compounds with the military top brass. His tour included a visit to Panmunjom, the truce village in the Demilitarized Zone, which was also the venue of some military conflicts, including the killing in 1976 of U.S. officers by North Korean soldiers with an ax.

South Korea usually ignores such snide remarks and military tours, brushing them aside as propaganda the North directs toward its domestic audience and its sympathizers in the South. But not on March 6, when President Lee summoned ministers dealing with foreign policy and national security to an unscheduled conference at the Blue House.

It was not known what military intelligence the president was privy to that prompted him to hold the conference. But the next day, the defense minister visited the marines stationed in an island in the sea off North Korea’s west coast and told them to shell the North Korean military units “10 times as much” in retaliation in case they were bombarded by them.

The defense minister was not alone in turning resolute against the North. The unification minister, who had remained conciliatory, calling for inter-Korean dialogue, joined him on the offensive when he denounced the North for failing to feed its residents properly. He said the North Korean authorities were held accountable for the plight of North Korean defectors, many of whom he said had been politically persecuted in addition to having been underfed.

Against this backdrop, U.S. President Barack Obama, who is coming to Seoul for a two-day summit on nuclear security, is set to visit the DMZ shortly after landing in Osan on Sunday. His DMZ visit is apparently intended to send a message to the North that the United States is firmly committed to the defense of South Korea as its military ally.

A security aide to Obama was quoted as saying, “It’s an important opportunity for him to meet with and see some of the American troops that are serving on the Korean Peninsula while also underscoring the strength of our alliance with the Republic of Korea and our strong commitment to their security.”

Obama is urged to articulate the U.S. commitment to South Korean security, not just when he visits DMZ, but when he meets President Lee on the sidelines of the nuclear summit. They also need to take up concrete measures for cooperation in defense against North Korea’s security threat, including the issue of extending the limits to the range and payload of South Korean-made ballistic missiles beyond the current 300 kilometers and 500 kilograms.

As Lee noted on Thursday, South Korea needs to develop longer-range missiles with heavier payloads as a convincing deterrent to an attack from North Korea, which has the entire South Korean territory within the range of the 1,000 missiles it reportedly holds in its possession.