Accusing the outside world of plotting against it, North Korea said Friday it had begun a "wartime mobilization" to defend itself from a military buildup by rival South Korea.

North Koreans scurried into underground air raid shelters as sirens wailed Friday across Pyongyang, a Western diplomat said.The announcement, which South Korea immediately downplayed, came as the rival Koreas, together with the United States and China, prepared for the resumption Monday of four-way talks intended to bring peace to the Korean peninsula.