North Korea has reacted angrily to a joint U.S.-South Korean military exercise that was held Friday, denouncing the use of its national flag as a target.

Around 2,000 South Korean and U.S. troops, along with jet fighters, tanks and attack helicopters took part in Friday's exercise to test responses to any assault. The exercise was timed to mark the 62nd anniversary of the start of the Korean War on June 25, 1950.

For the first time, an oversized North Korean flag was used in the live-fire exercise.

In a statement released Sunday, the North's state Korean Central News Agency called the move an extremely grave military action and politically-motivated provocation.

The statement blamed the United States for starting the war and expressed Pyongyang's intention to keep building its military.