North Korea fired what may be a ballistic missile on Tuesday, the Japanese coast guard said, the second apparent missile launch in less than a week after the reclusive state's leader urged the military to make more military advances.
South Korea's military also confirmed the launch of an "unidentified projectile," without elaborating.
Last week, North Korea said it fired a "hypersonic missile" that successfully hit a target on Wednesday.
The test launches by nuclear-armed North Korea underscored leader Kim Jong Un's New Year's vow to bolster the military to counter an unstable international situation amid stalled talks with South Korea and the United States.
The latest test came a day after the United States mission to the United Nations, joined by France, Ireland, Japan, the United Kingdom, and Albania, issued a joint statement condemning last week's test.
"These actions increase the risk of miscalculation and escalation and pose a significant threat to regional stability," U.S. Ambassador Linda Thomas-Greenfield said in the statement on Monday. Such tests not only improve the North's capabilities, but expands what it can offer illicit arms clients and dealers around the world, she added.
"(North Korea) makes these military investments at the expense of the well-being of the North Korean people," she said.
Thomas-Greenfield reiterated calls for North Korea to return to talks and abandon its missiles and nuclear weapons.
"Our goal remains the complete, verifiable, and irreversible denuclearization of the Korean Peninsula," she said.
South Korean military officials on Friday cast doubts on the capabilities of the "hypersonic missile" North Korea claimed to have test fired last week, saying it appeared to represent limited progress over Pyongyang's existing ballistic missiles.
U.N. Security Council resolutions ban all ballistic missile and nuclear tests by North Korea, and have imposed sanctions over the programmes.
North Korea has said it is open to talk, but only if the United States and others drop "hostile policies" such as sanctions and military drills.
Few observers expect Kim to ever fully surrender his nuclear arsenal. North Korea argues its missile tests and other military activities are for self-defence and are similar to those regularly undertaken by other nations.