North Korea informed Japan of military exercises by e-mail.

North Korea announced plans to conduct military exercises in the Sea of Japan, reported Reuters on June 22.
E-mail with the relevant staff members have received notification of the Japanese coast. The letter states that the exercises will take place from 25 June to 10 July 2009 in the coastal zone near the port of Wonsan. In this regard, said Pyongyang, coast near the port of Wonsan in the Sea of Japan will be closed to navigation, RIA Novosti adds.
The official response on the part of Japan has not yet been received. In Japan Coast service promised to consider carefully the information about the exercises in order to eventually develop a further plan of action.
West suggests that closing a portion of the Sea of Japan for navigation, Pyongyang plans to conduct new missile tests under the guise of military exercises. A similar prohibition of the DPRK government announced in mid-May, then had a water area of the Sea of Japan short-range missile launches. Nevertheless, in early June, when Pyongyang again banned foreign vessels from approaching the eastern coast, no launch has not been implemented.
The fears associated with nuclear and missile development of North Korea, intensified in May 2009, when Pyongyang conducted several tests, including a nuclear nature. In particular, the DPRK conducted an underground nuclear test, and launched several missiles, short-range actions. May 27, North Korea announced its withdrawal from the 1953 armistice that ended the Korean War.
Shortly thereafter, the UN Security Council adopted a new resolution tightening sanctions against Pyongyang. DPRK believes Washington is prepared to respond of the nuclear tests.