US National Security Advisor Jake Sullivan says the recent progress in Japan-South Korea ties is profoundly impacting the strength of their trilateral relationship.

He was speaking to reporters on Friday during a visit to Tokyo.

Sullivan commented on Washington's extended deterrence, defined as a commitment to defend allies with nuclear and conventional weapons.

He said the US will for the time being focus on deepening bilateral mechanisms with Japan and South Korea.

Sullivan added that Washington will at some point make a judgement regarding some kind of trilateral mechanism.

He also said China's buildup of nuclear weapons requires intense consultations among the world's nuclear powers.

Sullivan said the five permanent members of the United Nations Security Council should be engaged in that conversation, adding that the US and China should also hold bilateral discussions on disarmament and risk reduction.

Sullivan said US Secretary of State Antony Blinken will convey those views to China when he visits on Sunday and Monday.