PYONGYANG, Aug. 21 (Xinhua) -- The Democratic People's Republic of Korea (DPRK) Monday said the U.S.-South Korean joint military drill has plunged the Korean Peninsula into a critical phase.

The DPRK's state-run Korean Central News Agency (KCNA) said the scale of the U.S. military involvement in the exercise known as Ulchi-Freedom Guardian "far outnumbers the one in the last year."

"What is more serious is the fact that brass hats of the U.S. military, including the commanders of the U.S. forces in the Pacific and the Strategic Forces, visited South Korea on the eve of the rehearsal," the KCNA said.

"Even mercenaries from seven vassal countries, including Australia and Britain, have joined them," it added.

The United States and South Korea Monday kicked off their annual Ulchi-Freedom Guardian joint military drill amid high tension on the Korean Peninsula and repeated appeals for restraint on both sides by many countries.

Ulchi-Freedom Guardian is referred to a combined military exercise between the United States and South Korea, which is considered the world's largest computerized command and control implementation. The exercise was initiated in 1976 and is held annually during August or September.