Seoul, South Korea (CNN) -- U.S. and South Korean troops began a 10-day military exercise around Seoul on Tuesday, maneuvers the U.S. commander called "defense-oriented" during a period of heightened tensions with the communist North.
The annual "Ulchi Freedom Guardian" exercise involves about 530,000 troops from South Korea, the United States and seven other countries, as well as computer-aided simulations, the U.S. command in Seoul reported.
The joint U.N. command has notified its North Korean counterparts of the exercise, American military officials announced.
No peace treaty has formally ended the 1950-1953 Korean War, only an armistice that has left the peninsula split by the world's most heavily fortified border.
The secretive, economically stunted North Korea tested nuclear weapons in 2006 and 2009, while sporadic artillery duels and sea clashes still rattle the region.
Last week, South Korea fired at North Korea after it said northern gunners fired three shots close to its maritime border.
No casualties were reported.