North Korea's foreign ministry lashed out at the United States for not lifting sanctions against the country.
It said it had made various goodwill gestures but the United States was still following an "outdated acting script" and jeopardising any progress.
North Korea remains under a range of international and United States sanctions over its nuclear programme and projectile tests.
South Korea said that it has caught 3 companies importing coal and iron from North Korea in breach of United Nations sanctions.
The United States wants full nuclear disarmament before sanctions on the North can be lifted.