North Korea "is making it clear that its nuclear arms program is the essence of its national security and that it's not negotiable," said Sohn Yong-woo, a professor at the Graduate School of National Defense Strategy of Hannam University in South Korea.
Pyongyang conducted its third nuclear test in February, prompting a new round of U.N. sanctions that have infuriated its leaders. North Korea has since declared that the armistice ending the Korean War in 1953 is void, shut down key military phone and fax hotlines with Seoul, threatened to launch nuclear and rocket strikes on the U.S. mainland and its allies and, most recently, declared at a high-level government assembly that making nuclear arms and a stronger economy are the nation's top priorities.
The Korean Peninsula is technically is a state of war because a truce, not a peace treaty, ended the Korean War. The United States stations 28,500 troops in South Korea as a deterrent to North Korea.
Washington has said it takes the threats seriously, though White House press secretary Jay Carney said Monday the U.S. has not detected any military mobilization or repositioning of forces from Pyongyang.
The North's rising rhetoric has been met by a display of U.S. military strength, including flights of nuclear-capable bombers and stealth jets at annual South Korean-U.S. military drills that the allies call routine but that Pyongyang claims are invasion preparations.
South Koreans are familiar with provocations from the North, but its rhetoric over the last few weeks has raised worries.
"This is a serious concern for me," said Heo Jeong-ja, 70, a cleaning lady in Seoul. "The country has to stay calm, but North Korea threatens us every day."
Earlier Tuesday, a senior South Korean official told foreign journalists that there had been no sign of large-scale military movement in North Korea, though South Korea remains alert to the possibility of a provocation. The official spoke on condition of anonymity because he was not authorized to speak publicly to the media.