POCHEON, South Korea (Reuters) - The screech of incoming fire followed by an explosion resounds across forested hillsides near the border between North and South Korea. Battalion Commander Rob Kimmel of the U.S. 2nd Armored Brigade Combat Team, scanned the village at the base of a mountain for the tell-tale smoke.   That s enemy fire trying to attack R.O.K. forces located there,  says Kimmel - referring to South Korea by its official name, the Republic of Korea. This is a drill. It is just one of several that major world powers are engaged in on, over and near the Korean peninsula, amid heightened tension in the wake of North Korea s increasingly frequent missile tests and its sixth nuclear test this month. The U.S. soldiers are conducting a joint exercise with their South Korean allies, and the mission for the day is to recapture a village in enemy hands. There is an occasional crack of gunfire from soldiers in combat gear, hiding in the buildings, and prowling round corners of the village, which has been specially created for military  training. About 700 troops are engaged in the four-day drill, called Warrior Strike 8, near the Demilitarized Zone (DMZ) - the world s most heavily defended frontier. South Korea and the United States are technically still at war with North Korea after the 1950-53 Korean conflict ended with a truce, not a peace treaty. Such drills are held regularly, but the military has invited media to observe one for the first time in two years, said Kim Hyon-sok, public affairs specialist of the U.S. 2nd Infantry Division. The U.S. military has described the exercises as training for readiness  to fight tonight  against North Korea if needed. Based in Fort Hood, Texas, Kimmel s team is on a nine-month deployment in South Korea.  We are continuing to train for situations that may arise,  said Kimmel.  It s a big milestone type of exercise...we ll do two to three of these while we re here.  North Korea has repeatedly demanded that the United States and South Korea call off joint exercises, which Pyongyang view as provocative. A day earlier, U.S. and South Korean warplanes ran bombing drills over the peninsula. At the same, China s official Xinhua news agency reported that China and Russia began naval drills off the Russian far eastern port of Vladivostok, not far from the Russia-North Korea border. The Xinhua report did not link the exercises to the ongoing tensions over North Korea, which are expected to dominate the United Nations General Assembly in New York later on Tuesday. China and Russia have repeatedly called for a peaceful solution and talks to resolve a brewing crisis over North Korea.  Asked whether the drill near the border would make the North Korean side fearful of the allies military capabilities, Kimmel replied:  I m not sure, but I would hope they are.     