SEOUL, March 6 (Xinhua) -- The Democratic People's Republic of Korea (DPRK) test-fired four ballistic missiles into east waters early Monday as combined forces of South Korea and the United States launched their joint military exercises last week, the Joint Chiefs of Staff (JCS) of South Korea said.

The JCS was quoted by local media as saying that four ballistic missiles of an unidentified type were fired from an area near Tongchanri-ri in the DPRK's northwest region at about 7:36 a.m. local time (2236 GMT on Sunday).

The missiles flew about 1,000 km into the eastern waters.

Japanese Chief Cabinet Secretary Yoshihide Suga said three out of the four DPRK ballistic missiles fell into Japan's exclusive economic zone.

DPRK has not made any comment on the missile launch yet.

The Tongchang-ri is home to the DPRK's Sohae Satellite Launching Station where a long-range rocket was launched in February last year to put a satellite into orbit.

The February rocket launch followed the DPRK's fourth nuclear detonation in the previous month, which brought about the toughest-ever UN Security Council sanctions on Pyongyang. It was followed by the DPRK's fifth nuclear test in September last year.

The South Korean military is analyzing the missile launches jointly with the U.S. forces, maintaining a full defense readiness for any possible DPRK provocations, according to the JCS.

The DPRK's test-launches came in a possible retaliation to the annual U.S.-South Korea springtime war game that kicked off on March 1. Pyongyang has denounced it as a dress rehearsal for northward invasion.

The Foal Eagle field training exercise is scheduled to last by the end of April, mobilizing U.S. strategic assets such as a nuclear-powered aircraft carrier and stealth fighter jets.

On Feb. 12, the DPRK also test-fired a new type of Pukguksong-2 intermediate range ballistic missile (IRBM) in the launch supervised by top DPRK leader Kim Jong Un.

The IRBM, which was fired at an almost vertical angle of 89 degrees, blasted off to the highest altitude of 550 km and flew about 500 km. If it was launched at a normal angle, it would have traveled over 2,000 km, according to the South Korean intelligence agency's analysis.