US envoy Bill Richardson is travelling to North Korea at Pyongyang's request on an unofficial diplomatic mission to try to ease regional tensions.
Mr Richardson, who has been to North Korea several times in recent years, said he hoped to persuade the country's leaders to "calm down a bit".
Tensions have been especially high on the peninsula since the North shelled a South Korean island, leaving four dead.
The visit comes as the South staged its biggest ever civil defence drill. Read at BBC