( CNN ) -- North Korea fired 30 short-range rockets into the sea off the eastern coast of the Korean peninsula early Saturday , a South Korean defense ministry official said . The rockets have an estimated range of 60 km ( 37 miles ) , according to the ministry . North Korean officials did not send out a navigational warning to ships before the apparent test , the official said . It marks the fourth known rocket test by Pyongyang this month . The country fired 25 short-range rockets into the water earlier this week . The launches have drawn criticism from South Korea and the United States as provocations by the North . The U.S. and South Korea have been conducting a joint annual military drill since February , and North Korea has said its missile tests are a justifiable defensive reaction to them .
The rockets have an effective range of 100 miles , official says . The United States and South Korea criticize the tests as unnecessary . South Korea has said such tests are appropriate compared to U.S.-South Korean military exercises .