**FILE PHOTO** Two North Korean soldiers observe the south side as South Korean soldier stands... SEOUL (Reuters) - North and South Korean troops along their heavily fortified border exchanged gunfire for the first time in about a year, a military official said on Tuesday, with the incident coming as ties between the two have soured. North Korean troops fired two shots at a South Korean guard post near the Demilitarised Zone on Monday night and South Korean troops returned six shots, an official said by telephone. "No one was injured in the incident," the Joint Chiefs of Staff official said. One of the shots hit the guard post, causing South Korean troops to immediately return fire, the official said. Ties between the two Koreas had been warming in recent years as the two reached a number of agreements on economic cooperation and military confidence building. The last time there was an exchange of gun fire along the DMZ was in October 2005, the official said, when North Korea fired a bullet toward at a South Korean guard post and the South returned fire. The navies of the two had a major clash along a disputed maritime border in 2002, resulting in deaths and casualties on both sides. North Korea defied international warnings and test-fired seven missiles about a month ago. At an inter-Korean ministerial meeting in July, Seoul pressed Pyongyang to explain why it had launched the missiles. Seoul said it would suspend humanitarian aid until Pyongyang returned to stalled six-country talks on ending its nuclear weapons program. North Korean delegates stormed out of the meeting and said the South would "pay a price" for spoiling inter-Korean ties. Since then, North Korea has halted several projects with the South, including the reunions of families separated by the 1950-1953 Korean War. The two Koreas are technically still at war because the Korean War ended in a truce and not with a peace treaty. North Korea has stationed most of its 1.2 million-man army near the DMZ. South Korea has more than 650,000 troops, who are supported by about 30,000 U.S. troops.