Top U.S. officials have called North Korea’s nuclear threats a "serious" security challenge in the Indo-Pacific, and highlighted the strengthened security cooperation between South Korea, U.S. and Japan as a feat of the Biden administration’s Indo-Pacific diplomacy.

Secretary of State Antony Blinken, Defense Secretary Lloyd Austin, and National Security Advisor Jake Sullivan presented the stance in their joint contribution to The Washington Post.

In the article published on Monday, the U.S. officials described North Korea's nuclear saber-rattling and China's dangerous and provocative actions at sea as "serious" security challenges in the Indo-Pacific.

The three officials said that when President Biden took office, America's standing in this critical part of the world was at its lowest point in decades, and its allies and partners feared that the U.S. had become an unreliable friend.

The officials said that Biden, however, transformed the U.S. approach to the Indo-Pacific, which they claimed is the most important yet most undervalued feat of the Biden-Harris administration’s foreign and security policy. 

The officials also said that "President Biden brought together Japan and South Korea -- two countries with a difficult history -- to join the United States in the Camp David trilateral summit," through which the three nations formed unprecedented economic and defense cooperation.