South Korea and the U.S. began a joint exercise in the East and Yellow Seas Monday amid heightened tensions over the possibility of a fresh provocation by North Korea. 

U.S. strategic military assets, including a nuclear-powered aircraft carrier and an attack submarine, have gathered in South Korea for the drill. 
 
The U.S. nuclear-powered carrier, the USS Ronald Reagan (CVN-76) arrived in South Korea on Sunday, carrying 70 aircraft such as FA-18 Super Hornets.
 
The 333-meter-long, 100-thousand-ton Nimitz-class carrier will take part in the joint drill set for Monday to Friday.
 
The U.S. special operations forces reportedly on board a submarine belonging to the USS Ronald Reagan-led strike group will participate in a simulated counterattack against North Korean soldiers.
 
The Ohio-class guided-missile submarine USS Michigan (SSGN-727) already arrived at the southern port of Busan on Friday as part of a regularly scheduled deployment to the Western Pacific. 
 
The submarine will also join the exercise along with the South Korean Navy's 76-hundred-ton Sejong the Great destroyer and warships. 
 
During the joint exercise, which will involve about 40 naval vessels from the two sides, the Joint Surveillance Target Attack Radar System -- an airborne battle management aircraft -- will also be deployed to monitor North Korea's ground force movements and coastal artillery.