The launch comes a day after North Korea said the US was within strike range
North Korea has fired an "unidentified projectile," according to South Korea's military.
The projectile was fired from Pukchang in south Pyongan province, the Joint Chiefs of Staff said in a statement reported by the Yonhap news agency.
The area, which is the location of a military airport, is north of the capital Pyongyang.
It was not believed to be a intercontinental ballistic missile, an anonymous military source told Yonhap.
The launch comes a day after North Korea said the US was within strike range and claimed it has "all kinds of powerful means for annihilating retaliatory strikes."
Earlier this month, North Korea launched a medium long-range ballistic missile called the Hwasong-12, which it said was capable of carrying a heavy nuclear warhead.
That missile - which was launched from a site in Kusong, North Pyongan - flew for about 30 minutes, travelling about 500 miles (800km) before landing in the Sea of Japan, according to Tokyo.
North Korea regularly tests short-range missiles, but it is also said to be working to master the technology needed to field nuclear-tipped missiles that can reach the US mainland.
The launch of the Hwasong-12 was the 10th test this year.