North Korea fired more projectiles into the sea on Friday hours after deriding South Korea for taking part in ongoing military drills with the U.S. It was the latest in a series of launches since July 25 that have included the test firing of a new missile system.

South Korea's Joint Chiefs of Staff said at least two projectiles were launched from an area on the North's eastern coast and flew for about 143 miles before splashing down between the North Korean and Japanese coasts.

The Joint Chiefs said it remained unclear whether it was rockets or missiles fired on Friday.

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CBS News' Jen Kwon notes that the most recent missiles test-fired by North Korea were believed to have been based on Russia's 9K720 Iskander, a mobile short-range ballistic missile system. Projectiles launched on July 31 and August 2 were likely an upgraded version of that missile system.

Shortly before news of the latest launches, North Korea's government released a statement via state-run news outlet KCNA condemning joint military exercises by South Korea and the U.S., and saying Kim Jong Un's regime believes there is "nothing more to talk about with the South Korean authorities," and that it has no more "plans to sit with them."

A senior Trump administration official said the U.S. was "aware of reports of a missile launch from North Korea, and we continue to monitor the situation. We are consulting closely with our Japanese and South Korean allies."

Japan's Defense Ministry said the North Korean projectiles did not reach the country's territorial waters or its exclusive economic zone.

Kwon said Japanese Prime Minister Shinzo Abe confirmed the new launches, but said they did "not affect the security of Japan." Abe added that he would "make every possible effort" to protect his people, working in close cooperation with the United States and other regional countries.

South Korea's presidential office said national security adviser Chung Eui-yong presided over an emergency National Security Council meeting about the launches, and President Moon Jae-in was briefed on the developments.

Leverage building?

The North Korean missile tests, which President Trump has repeatedly played down, come amid stalled diplomatic talks with the U.S. on the North's nuclear program. So far, North Korea has stuck by its unilateral suspension of nuclear and long-range missile tests, which came during a diplomatic outreach to Washington last year.

The North has been conducting a slew of short-range ballistic tests in recent weeks in what is seen as an effort to build leverage ahead of negotiations with the U.S., which may resume sometime after the end of joint U.S.-South Korea military drills later this month.

Professor Kim Youngjun, who teaches military strategy at the Korea National Defense University and serves as an adviser to the South Korean government, told CBS News' Kwon that the launches do appear to be aimed at bolstering the North's negotiating position if and when talks resume. He also said the launches could just be part of Pyongyang's "ordinary weapon system schedule" of testing.

The statement released by North Korea's Committee for the Peaceful Reunification of the Country just before the launches came on the heels of a speech in which Moon said that momentum for dialogue remained alive, despite the series of "worrying actions taken by North Korea recently."

The North said Friday that It would be "senseless" for Moon to believe that inter-Korean dialogue would automatically resume after the U.S.-South Korea military drills.