North Korea fired two unidentified projectiles eastward from Koo Song, about 50 miles from Pyongyang, around 4:30 p.m. local time, South Korean officials said.
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South Korea's Joint Chiefs of Staff confirmed the launch on Thursday but had no additional details immediately available. The South's military is analyzing the short-range launch, North Korea's second in less than a week.
"At the moment, our army has strengthened surveillance and is at alert together with the U.S.," Korean officials told ABC News.
That act, a "barrage" of projectiles launched into the Sea of Japan, later was described as a regular, defensive military exercise.
That happened on Saturday around 9 a.m. local time, after which White House press secretary Sarah Sanders said, "We are aware of North Korea's actions tonight. We will continue to monitor as necessary."
South Korea's Joint Chiefs of Staff said in a statement at the time that "our military is strengthening its surveillance and border in preparation for further launch of North Korea."
"Korea and the United States are working closely together to maintain their ready preparedness," the statement continued.
Former State Department official Stephen Ganyard, an ABC News contributor, said after Saturday's launch that long-range missiles remain a much larger threat.
"I don't think we should get too excited about a short-range test unless someone can tell us that it was a long-range test that failed," Ganyard said. "A short range test is Kim demanding attention, not making a statement."
That launch was the first for North Korea since Nov. 28, 2017, however, that was a long-range missile.