The U.S. State Department said Friday that Deputy Secretary of State John Sullivan spoke by phone with South Korea's newly appointed Vice Foreign Minister Cho Sei-young and reaffirmed their commitment to the final, fully verified denuclearization of North Korea.

In a press release that offered new details of the conversation following an earlier description released by Seoul's Foreign Ministry, the department said Sullivan and Cho reaffirmed a commitment to trilateral cooperation with Japan and agreed to continue to work closely together to address common security challenges in the Indo-Pacific region. 

The State Department has recently emphasized the need for three-way cooperation between Seoul, Washington and Tokyo.

Earlier this week, department spokesperson Morgan Ortagus said that stronger trilateral cooperation will also be discussed when President Donald Trump holds summit talks with Japanese Prime Minister Shinzo Abe on the sidelines of the G20 summit scheduled in Osaka at the end of this month.