North Korea launched approximately 10 short-range ballistic missiles toward the sea on Thursday, South Korea's military said, one day after Pyongyang dismissed Donald Trump's decision to curtail joint military exercises with Seoul in what appeared to be an attempt to revive diplomacy.

South Korea's joint chiefs of staff said the missiles were fired from the Pyongyang region at around 5 p.m. local time (08:00 GMT) and traveled toward North Korea's eastern waters.

The military said South Korea had strengthened its surveillance and was closely coordinating information on the launches with the United States and Japan. Japan's prime minister's office also confirmed it had detected a suspected missile launch.

South Korea's presidential national security council convened an emergency meeting in response. It subsequently issued a statement urging North Korea to cease ballistic missile launches, which are prohibited under UN Security Council resolutions.

On Wednesday, the South Korean and US militaries announced they were scaling back their 11-day Ulchi Freedom Shield exercises. Trump had ordered the Pentagon to "substantially reduce" the drills just before they began on Monday. The US president cited what he described as a good relationship with North Korean leader Kim Jong-un, as well as South Korea's refusal to support him over the war against Iran.

Kim Yo-jong, the influential sister of the North Korean leader, dismissed Trump's overture on Wednesday, calling it unworthy of comment.

"The provocative, aggressive nature of the drills won't change even though their duration and size were reduced," she said. "If the US calculates that it can propagate its recent measure as one of so-called good faith, they will not get the desired answer."

She pointed to a series of other military exercises conducted by the US and South Korea earlier this year, as well as Seoul's push to acquire nuclear-powered submarines.

Despite her criticism, Kim Yo-jong stopped short of the fiery rhetoric typical of North Korean statements. She said personal relations between her brother and Trump were "still excellent," a signal that Pyongyang may be waiting for larger concessions from Washington before returning to talks.

She also denied Trump's claim that Kim Jong-un had responded to his request for a conversation.

When asked by reporters on Wednesday whether he would meet Kim Jong-un this year, Trump said: "Yeah, I will be." He declined to answer whether he was exchanging letters with Kim, but said he got along with him.