North Korea fired four short-range missiles toward the Sea of Japan, South Korea's Foreign Ministry said Saturday. The missiles were apparently Scud-type missiles, estimated to have a range of about 500 kilometers (310 miles), said South Korea's Yonhap news agency. South Korean intelligence estimates that North Korea has about 700 such missiles in its arsenal. Pyongyang test-fired four such missiles off the east coast on Thursday, Yonhap reported. North Korea had issued a warning to mariners to avoid an area in the Sea of Japan at certain times between June 24 and July 9 because of a "military firing exercise," according to a U.S. military communication about the warning provided to CNN.