U.S. Secretary of Defense Pete Hegseth speaks during a press conference with U.S. President Donald Trump (not pictured) called in response to the fatal collision of a passenger airplane and a U.S. military helicopter last night, at the White House in Washington, D.C., U.S., Jan. 30. EPA-Yonhap

South Korea's acting Defense Minister Kim Seon-ho and new U.S. Defense Secretary Pete Hegseth held their first phone call Friday and reaffirmed the steadfast alliance between the two nations, Seoul's defense ministry said.

In the phone conversation, both sides concurred on the need to advance and deepen the level and scope of their bilateral alliance, which has stood as a "linchpin" for peace and stability on the Korean Peninsula and in the region over the past 70 years, the ministry said.

Hegseth reaffirmed the U.S. ironclad commitment to defending South Korea and vowed to closely cooperate with Seoul to cement the bilateral alliance, it added.

Noting North Korea's evolving nuclear and missile threats, the defense chiefs agreed that sustaining the alliance through their combined defense posture is more "important than ever" to effectively deter and respond to such threats.

For such a purpose, they agreed to continue to maintain and advance their trilateral security cooperation, also involving Japan, on the back of the South Korea-U.S. alliance.

The defense chiefs expressed concerns over North Korea and Russia's deepening military alignment, pledging to respond to the global security threat together with the international community.

Hegseth took office last week as the first defense secretary in the second term of U.S. President Donald Trump, who returned to the White House earlier this month. (Yonhap)