(CNN) -- The United States and South Korea began their annual joint military exercise Monday, kicking off an 11-day drill designed to ensure the countries' alliance is "fully prepared to respond to any potential provocations," according to a statement from U.S. forces in South Korea.
On Monday, South Korean president Lee Myung-bak ordered his military to "thoroughly" prepare with the United States to counter threats from North Korea, the Yonhap news agency reported.
The timing of the joint training comes during a time of increased military tensions. South Korea blamed North Korea for sinking a 1,200-ton warship in March, killing 46 sailors. North Korea denied it sunk the ship.
North Korea said Sunday that it will "deal a merciless counterblow to the U.S. imperialists" and to South Korean "traitors," in response to the U.S.-South Korea joint military exercise.
"The military counteraction of the DPRK [Democratic People's Republic of Korea] will be the severest punishment no one has ever met in the world," a spokesman for the General Staff of the Korean People's Army said in a statement carried by North Korea's official news agency.
North Korea's statement Sunday took direct aim at U.S. President Barack Obama. CNN
