North Korea test fires a new weapon, in this undated photo released on August 11, 2019 by North Korea's Korean Central News Agency (KCNA).

South Korea's military says North Korea fired more projectiles into the sea to extend a recent streak of weapons tests believed to be aimed at pressuring Washington and Seoul over slow nuclear diplomacy.

South Korea's Joint Chiefs of Staff said projectiles were twice launched from an area on the North's eastern coast, but didn't immediately say what the weapons were, how many were launched or how far they flew.

"North Korea fired two unidentified projectiles on Friday morning KST (Korea Standard Time) from Tongchun area in Gangwon Province in North Korea into the East Sea," said the office of South Korea's Joint Chief of Staff in a text briefing, according to NBC News.

"Our military is monitoring over any possible development and additional launching of projectiles by North Korea while maintaining military readiness," the office said.

It was North Korea's sixth round of weapons launches since late July when it began stepping up its weapons demonstrations while expressing frustration over stalemated nuclear negotiations with the United States and continuance of U.S.-South Korea joint military drills that the North sees as an invasion rehearsal.

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

Japan's Defense Ministry said the North Korean projectiles did not reach the country's territorial waters or its exclusive economic zone. The White House said it was aware of reports of the launches and was consulting with Seoul and Tokyo.

The weapons the North tested in recent weeks included a new rocket artillery system and what security analysts say are two new short-range mobile ballistic missile systems that would potentially expand the North's ability to strike targets throughout South Korea, including U.S. bases there.

Experts say President Donald Trump's downplaying of the North's launches allowed the country more room to intensify its testing activity while it seeks to build leverage ahead of a possible resumption of negotiations, which could happen sometime after the end of the allied drills later this month.

The North has ignored South Korean calls for dialogue recently and is seen as dialing up pressure on Seoul to coax major concessions from Washington on its behalf.

The Joint Chiefs of Staff alerted reporters to the launches hours after the North issued a statement berating South Korea, saying it's "senseless" for Seoul to hope for a resumption of inter-Korean dialogue while it continues its military exercises with the United States.

The statement by the North's Committee for the Peaceful Reunification of the Country came a day after Moon said in a speech that the momentum for dialogue remains alive despite the series of "worrying actions taken by North Korea recently."

"A sure thing is that the (South) Korean chief executive is (such a) funny man as he just reads what was written by his juniors," the statement said while avoiding calling Moon by his name.

It would be "senseless" for Moon to believe that inter-Korean dialogue will automatically begin after the end of U.S.-South Korea military drills, the statement said.

The North had recently said it plans to talk only with Washington and not Seoul, and that inter-Korean dialogue won't resume unless South offers a "plausible excuse" on why it keeps hosting military drills with the United States.

— CNBC contributed to this report.