"These launches are clear violations of multiple United Nations Security Council resolutions, and demonstrate the threat (that North Korea's)... unlawful weapons of mass destruction and ballistic missile programs pose to the region," the statement said.

North Korea fired two short-range ballistic missiles, South Korea's military said Thursday, shortly after Pyongyang warned of an "inevitable" response to ongoing US-South Korea joint military drills.

The trilateral statement reflected the growing thaw between Japan and South Korea -- a major foreign policy goal of President Joe Biden's administration as it strengthens alliances in a region tested by North Korea and expansionist China.

"The United States reaffirms unequivocally its ironclad security commitments to both Japan and the ROK," as South Korea is officially known, the statement said.

It noted that US National Security Advisor Jake Sullivan met Thursday in Tokyo with his Japanese and South Korean counterparts "to further strengthen trilateral cooperation, including through lock-step coordination in responding to the threats" from North Korea.

The statement underscored that the trilateral alliance's "cooperation would not be shaken by provocations."