South Korea's Joint Chiefs of Staff said it had detected what it presumed were two short-range ballistic missiles (SRBMs) launched eastward from North Pyongan Province on the west coast of North Korea.
Japan's coast guard also reported that the North fired what could be a ballistic missile.
The missiles appeared to have landed in the sea outside Japan's exclusive economic zone, broadcaster NHK reported, citing an unnamed Japanese defence ministry official.
The launch would be the third since New Year's day, an unusually high pace of missile tests. The previous two were of "hypersonic missiles," North Korean state media reported, capable of high speeds and manoeuvring after launch.
In contrast to Friday's tests, each of those earlier launches involved a single missile which were fired from Jagang Province, neighbouring North Pyongan.
Kim Dong-yup, a former South Korea Navy officer who teaches at Seoul's Kyungnam University, said North Korea could have fired previously deployed SRBMs such as the KN-23 or KN-24.
"It could fit in their ongoing winter exercises, while sending a message to the United States through action following the state media statement," he said.
North Korea defended the missile tests as its legitimate right to self-defence and said the United States was intentionally escalating the situation by imposing new sanctions, state media reported earlier on Friday, citing the foreign ministry.
North Korea's recent development of a "new-type weapon" was just part of its efforts to modernise its national defence capability, and did not target any specific country or harm the security of neighbouring countries, the foreign ministry said in a statement on the KCNA state news agency.
The statement warned of an unspecified "stronger and certain reaction" if the United States adopts a confrontational stance.
The administration of US President Joe Biden on Wednesday imposed its first sanctions over North Korea's weapons programs following a series of North Korean missile launches.
It also called on the United Nations Security Council to take action against several North Korean individuals and entities accused of violating security council resolutions that ban North Korea's missile and nuclear weapons development.
US Secretary of State Antony Blinken said the United States had made clear it had no hostile intent toward North Korea and was willing to engage in talks without preconditions, but that the tests were "profoundly destabilising."
The North Korean foreign ministry said that while Washington may talk of diplomacy and dialogue, its actions show "it is still engrossed in its policy for isolating and stifling" North Korea.
"The US is intentionally escalating the situation even with the activation of independent sanctions, not content with referring the DPRK's just activity to the UN Security Council," the statement said.
Kim Dong-yup pointed to remarks last year by North Korean leader Kim Jong-un that Pyongyang will approach Washington "on the principle of answering force with toughness, and good faith in kind".
