South Korean troops fired artillery and dropped sonar buoys into the Yellow Sea as naval drills kicked off Thursday near the spot where a warship sank four months ago. Some 4,500 South Korean troops aboard more than 20 ships and submarines as well as about 50 aircraft were mobilized to take part in the five days of naval exercises off the west coast, including spots near the two Koreas' maritime border, the Joint Chiefs of Staff said. North Korea called the drills a military provocation that threatened to re-ignite war on the Korean peninsula. “If the puppet warmongers dare ignite a war, (North Korea) will mercilessly destroy the provokers and their stronghold by mobilizing most powerful war tactics and offensive means beyond imagination,” the ruling Committee for the Peaceful Reunification of the Fatherland said in a statement carried by North Korea's official Korean Central News Agency. KCNA reiterated the committee's message in a separate report later Thursday, warning North Korea will retaliate at “even the slightest sign of attack.” Soldiers aboard the 14,000-ton ROK Dokdo, an amphibious landing ship, patrolled the deck as Lynx helicopters dropped sonar devices into the sea in search of enemy submarines. A 1,200-ton frigate remained on standby, ready to bomb the target. The fleet dispatched for the exercises also include three 1,800-ton submarines, a 4,500-ton destroyer, and some 50 fighter jets, Cmdr. Won Hyung-sik of the Joint Chiefs of Staff said in Seoul. The drills come just weeks after South Korea's joint military exercises with the U.S. off the east coast - maneuvers held in response to the deadly March sinking of the Cheonan warship, which killed 46 South Korean sailors. A five-nation team of investigators concluded in May that a North Korean torpedo fired from a submarine sank the 1,200-ton Cheonan as the warship carried out routine surveillance. North Korea denied sinking the ship.