The unidentified projectiles launched by North Korea early were ballistic missiles that flew about 250km, South Korea's Joint Chiefs of Staff says.
The projectiles appeared to be a different type to previous launches, minister Jeong Kyeong-doo said, according to South Korean news agency Yonhap.
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Japan's defence minister said any ballistic missile launch by North Korea would violate United Nations resolutions, Japan's Kyodo news agency reported.
The latest launches early on Wednesday were from the Hodo peninsula on North Korea's east coast, the same area from where last week's were conducted, the JCS said in a statement.
It said it was monitoring the situation in case of additional launches and maintaining a readiness posture.
North Korea test-fired two new short-range ballistic missiles on July 25, its first missile tests since leader Kim Jong-un and US President Donald Trump met in late June and agreed to revive stalled denuclearisation talks.
The White House, the Pentagon and the US State Department did not immediately respond to requests for comment.
Both Trump and US Secretary of State Mike Pompeo played down last week's launches and Pompeo has continued to express hope for a diplomatic way forward with North Korea.
Since the June 30 meeting in the Demilitarised Zone (DMZ) between the two Koreas, Pyongyang has accused Washington of breaking a promise by planning to hold joint military exercises with South Korea in August and warned that these could derail any dialogue.
North Korea has also warned of a possible end to its freeze on nuclear and long- range missile tests in place since 2017, which Trump has repeatedly upheld as evidence of the success of his engagement with Kim.