(CNN) -- The United States and Japan started joint military exercises Friday, the Japanese defense ministry said, as tensions simmered on the Korean peninsula.
About 10,500 U.S. service members are taking part in the drills, officials said.
The "Keen Sword" exercise will continue until December 10 on military sites in Okinawa, mainland Japan and the waters surrounding it, according to officials.
"Keen Sword will cap the 50th anniversary of the Japan-U.S. alliance as an 'alliance of equals,'" said Maj. William Vause, chief of operational plans, training and exercises. "It is the largest bilateral exercise between the United States and Japan military forces. [The exercise] will better enhance both of our countries' readiness to respond to varied crisis situations."
The drill is not directed to any nation, officials said.
"The goal of Keen Sword is to increase and improve our bilateral relationship to further enhance the Japan and U.S. alliance," Vause said, "and to provide a realistic training environment that allows Japan Self Defense Force and U.S. forces to respond to a wide range of situations."
The drill starts days after South Korea and the United States wrapped up joint military exercises on the Yellow Sea.