U.S. and South Korean defense officials have said they've seen nothing to indicate that Pyongyang is preparing for a major military action, and there was no sign of an exodus of foreign companies or tourists from South Korea.
Still, the United States and South Korea have raised their defense postures, as has Japan, which deployed PAC-3 missile interceptors in key locations around Tokyo on Tuesday as a precaution against possible North Korean ballistic missile tests.
In Rome, U.N. Secretary-General Ban Ki-moon described the tensions on the Korean Peninsula as "very dangerous" and said that "any small incident caused by miscalculation or misjudgment" may "create an uncontrollable situation."
Also Tuesday, North Korea pulled out more than 50,000 workers from the Kaesong industrial park, which combines South Korean technology and know-how with cheap North Korean labor. It was the first time that production has been shut down at the complex, the only remaining product of economic cooperation between the two countries that began about a decade ago when relations were much warmer.
Other projects from previous eras of cooperation such as reunions of families separated by war and tours to a scenic North Korean mountain stopped in recent years.
Associated Press writers Hyung-jin Kim in Seoul, South Korea, and Nicole Winfield in Rome contributed to this report.