SEOUL – South Korea’s presidential office condemned North Korea’s launch of more than 10 short-range ballistic missiles on Aug. 20 and ordered its military to maintain full readiness during ongoing joint exercises with the United States.

The launch came after North Korea’s Kim Yo Jong, sister of Kim Jong Un, on Aug. 19 condemned the U.S.-South Korea military drills, despite U.S. President Donald ​Trump’s order to ​substantially reduce U.S. participation ⁠in the exercises.

The presidential office convened an emergency security meeting attended by officials from the defense ministry and military authorities after North Korea fired the missiles from the Pyongyang area toward the sea to the east of the Korean Peninsula, it said in a statement.

“The ballistic missile launch is a grave act that violates U.N. Security Council resolutions,” it said, calling on North Korea to immediately halt such actions.

The missiles flew around 186 miles toward the sea, South Korea’s Joint Chiefs of Staff said.

South Korean defence minister Ahn Gyu-back told lawmakers that the short-range ballistic missiles are believed to be 600 mm multiple rocket launchers, adding that Seoul has been tracking them because they could be potentially deployed near its border with the South.

North Korea has previously described the 600 mm system, known externally as the KN-25, as being able to deliver tactical nuclear warheads.

Ahn said earlier in the day that North Korea possesses between 80 and 120 nuclear warheads.

Military drills by South Korea and the U.S. were cut short to end on Friday after President Donald Trump ordered a substantial reduction in U.S. participation and said he wanted to revive diplomacy with North Korean leader Kim Jong Un. ⁠

Trump ​said on Aug. 17 he had received a response ​from North Korean leader Kim Jong Un after the reduction. But Kim’s sister, Kim Yo Jong, said on Aug. 19 she was unaware of any recent communications between the two countries’ leaders, while saying the United States’ “hostile policy” towards North Korea had not changed.

Yang Moo-jin, a professor at the University of North Korean Studies in Seoul, said the launch appeared aimed at underscoring that Kim Yo Jong’s warning a day earlier was “not mere rhetoric.”

He said the launch likely served multiple purposes, including signalling opposition to the South Korea-U.S. military exercises, expressing displeasure over recent discussion of North Korea’s nuclear arsenal, and warning outside powers against speculation about Pyongyang’s security affairs.

“It is a message that matters concerning North Korea’s security are for North Korea to decide,” Yang said, adding the launch could also have been used to test improved missile systems.

Chinese Foreign Minister Wang Yi, who visited Seoul this week, urged South Korea not to take sides between Beijing and Washington, saying the U.S. should abandon its “hostile” policy toward North Korea to ease tensions on the Korean Peninsula.