MOSCOW, August 18 (RIA Novosti) - North Korea on Monday ordered its troops onto a state of full combat readiness as the United States and South Korea started military drills, Yonhap reported, citing the North's official KCNA agency.

The South Korean news agency said an English language KCNA report on the military order warned of a "merciless" response to any aggression that could include the country's "nuclear deterrent."

Seoul and Washington say the exercises are purely defensive.

The latest rhetoric over the military drills, which followed a threat on Sunday to "wipe from the face of the earth" the United States and South Korea, comes amid a reported thaw in cultural ties between the two Koreas.

North Korea and South Korea's Hyundai Group on Monday agreed to resume tourist trips to Mount Kumgang in the northeast of the peninsula and the North's border town of Kaesong, Yonhap reported.

"Both sides decided to resume the suspended tours to Mount Kumgang as soon as possible and launch the tour of Pirobong, the highest peak on the mountain," said a joint press release issued by Hyundai and the North's Korea Asia-Pacific Peace Committee, which handles inter-Korean business ties.

"Both also agreed to resume tours of Kaesong soon and to energize the operations of the Kaesong Industrial Zone as the land passage through the MDL [Military Demarcation Line] is put back on a normal basis," the release quoted by Yonhap said.

The deal was announced following a meeting on Sunday between North Korean leader Kim Jong-il and Hyundai chair Hyun Jeong-eun in Pyongyang, and the release last Thursday of a Hyundai worker held for months accused of criticizing the country's political system.

Former U.S. President Bill Clinton visited Pyongyang earlier in August and secured the release of two U.S. journalists sentenced to 12 years hard labor for illegal entry into North Korea and engaging in "hostile acts."