US Edition 
Japan and US start biggest ever joint military exercise
Japan and the United States have started their biggest ever joint military exercise amid rising tensions on the Korean peninsula.
The week-long drill, named Keen Sword 2011, will involve more than 44,000 personnel from the militaries of both nations as well as 60 warships and more than 400 aircraft, US officials said.
Underlining the show of force in the region, South Korea's military has been invited to attend the exercise as an observer for the first time.
Keen Sword is being staged immediately after the US and South Korea conducted manoeuvres off the west coast of the Korean peninsula, close to the island where four people were killed in November by a North Korean artillery barrage.
The annual exercise was planned well in advance of the attack on South Korea and is designed to "better enhance both of our countries' readiness to respond to varied crisis situations," said Major William Vause, head of operational training.
"Keen Sword will cap the 50th anniversary of the Japan-US alliance as an 'alliance of equals,'" said Major Vause, who is based at Kadena Air Base in Okinawa. "It is the largest bilateral exercise between the United States and Japan military forces."
The drills that are scheduled to take place include close-air support practice, live-fire training, search and rescue, integrated air and missile defence and base security. Given concerns over North Korea's alleged efforts to sell its nuclear and missile technology, maritime defence and interdiction drills have been added to the exercise.
The forces of all three nations have been on high alert since the sinking of the South Korean warship the Cheonan in March and the involvement of South Korean observers is designed to demonstrate Japan's support for its neighbour and, potentially, win Seoul's backing in Tokyo's efforts to limit China's efforts to claim sovereignty over disputed islands in the Okinawa chain.
The nuclear powered aircraft carrier USS George Washington will be taking part in the exercise, which also marks the 50th anniversary of the Japan-US alliance.