A U.S. official confirmed to ABC News on Thursday that the short range missiles had not been seen before.
"North Korea today launched two unidentifiable objects at 5:34 and 5:57 am," according to a statement from South Korea's Joint Chiefs of Staff.
The flight distance of the first missile was approximately 430 kilometers (265 miles), while the second flew about 690 kilometers (428 miles). Both flew at an altitude of about 50 kilometers, South Korea's Joint Chiefs of Staff said.
Earlier, when the South Korean military had tracked the first launch, the statement said, "Our military is keeping close watch in case of additional launches."
The missiles were fired from Wonsan in eastern North Korea and landed in the Sea of Japan.
Two U.S. officials confirmed to ABC News that North Korea had fired at least one short-range projectile. One of the officials characterized it as a short-range missile.
"We've found some features that indicate that the second one could be a new type, which requires more analysis and assessment," South Korea's Joint Chiefs of Staff said in a statement. "It is too early to tell whether these were ballistic missiles or not."
South Korea's National Security Council later confirmed both missiles were a new type of short-range missile.
"We believe that Kim Jong Un has recently stayed in the region, and summertime military drills are now under way in the North," according to the South Korean Joint Chiefs of Staff.
Earlier, another official said the latest launch appeared similar to the two short-range missiles fired by North Korea on May 9. Those missiles traveled similar distances, but were not intercontinental ballistic missiles (ICBMs) that are of most concern to U.S. officials.
President Donald Trump downplayed the launches in May that would have been violations of United Nations Security Council resolutions.
"My people think it could have been a violation, as you know," he said at the time. "I view it differently."
Following Trump's meeting with North Korean leader Kim Jong Un in Singapore last year, Kim committed to not conducting ICBM launches or nuclear tests while the U.S. and North Korea engaged in discussions towards a possible denuclearization deal.
On Monday, Trump reaffirmed to reporters that North Korea had continued to abide by Kim's personal commitment.
"Our relationship with North Korea has been very good. We've really established a good relationship with Kim Jong Un," said Trump. "There's no rocket testing. There's no missile testing. We're getting our remains back. We got our hostages back. And we have a very, very good relationship, the two of us, and that's very important."
Following Trump's June 30 meeting with Kim at the Demilitarized Zone (DMZ) dividing South Korea and North Korea U.S. officials hoped that working level talks between the U.S. and North Korea would resume after the failure of the Trump-Kim meeting in Hanoi, Vietnam.
But last week, North Korea hinted that those talks might not occur if the U.S. went ahead with a scheduled military exercise with South Korea in August.