Pyongyang fired two missiles just hours after criticising a US push for new sanctions over the previous launches as a "provocation" and warning of a strong reaction.
North Korea has fired at least two ballistic missiles, its third test in two weeks, just hours after criticising a US push for new sanctions over the previous launches.
The short-range ballistic missiles fired on Friday flew 430 kilometres (267.2 miles) and reached the apogee of 36 kilometres (22.4 miles), South Korea's military said.
The new test comes after the United States imposed new sanctions this week, prompting Pyongyang to vow never to give up its "right to self-defence".
Japan's coast guard said it had detected "the launch from North Korea of what appears to be a ballistic missile or missiles at 14h55".
Yang Moo-jin, a professor at the University of North Korean Studies, said that the timing of the latest suspected test was concerning.
"This situation is worrisome. North Korea launched this test right after releasing a statement saying they are not going to give up their 'right to self-defence,'" Yang said.
Despite biting international sanctions over its nuclear weapons programme, Pyongyang tested what it said were hypersonic missiles on January 5 and January 11.
After the second test, which was personally supervised by leader Kim Jong-un, the United States imposed additional sanctions on five people linked to North Korea's ballistic weapons programme.
The move prompted accusations from a foreign ministry spokesman in Pyongyang that the United States was "intentionally escalating" the situation.
If "the US adopts such a confrontational stance, the DPRK will be forced to take stronger and certain reaction to it," the spokesman said in comments carried by state news agency KCNA earlier on Friday.
On Thursday, US Secretary of State Antony Blinken called on North Korea to sit down for talks with the United States, which he said harboured no "hostile intent" toward Kim Jong Un's regime.
The continued tests are "profoundly destabilising, it's dangerous, and it contravenes a whole host of UN Security Council resolutions," Blinken said in a televised interview.