-- North Korea also is believed to have pursued a biological weapons program since the 1960s.
-- The huge number of North Korean troops and weapons arrayed close to the Demilitarized Zone, a buffer area between the two Koreas. In the early hours of a conflict, North Korea could rain thousands of rounds of artillery on Seoul, the South Korean capital, only 64km south of the border.
With more than 1 million soldiers, North Korea has one of the largest armies in the world. However, the country is short of food and fuel, and many of its weapons are antiquated. Its air force, for example, has as many as 1,600 planes, but most are based on old Russian and Chinese designs from the 1950s and 1960s.
Still, North Korea often showcases its military at politically sensitive times. In March, four communist fighter jets intercepted a US reconnaissance plane off the North's east coast. The fighters illuminated the US plane with targeting radar, but there was no hostile fire.