Retired Navy Adm. Harry Harris was sworn in on Saturday as the United States's new ambassador to South Korea, taking the role at a tumultuous time on the Korean Peninsula.

Harris, who previously served as the commander of U.S. forces in the Pacific, was confirmed by the Senate on Thursday in a voice vote.

Secretary of State Mike Pompeo Michael (Mike) Richard PompeoTreasury sanctions individuals, groups tied to Russian malign influence activities Navalny released from hospital after suspected poisoning Overnight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers MORE congratulated Harris on his swearing in on Saturday, writing in a tweet that he has "a lot of work ahead" of him.

Congratulations to Harry B. Harris, Jr. on his swearing in as the next U.S. Ambassador to South Korea. A lot of work ahead on maintaining our ironclad alliance with #ROK and achieving the final, fully verified denuclearization of the #DPRK, as agreed to by Chairman Kim. pic.twitter.com/ixacGezBT3 — Secretary Pompeo (@SecPompeo) June 30, 2018

Harris is taking on the role at a pivotal moment for U.S. involvement on the Korean Peninsula and in East Asia, more broadly.

His swearing in comes less than three weeks after President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE met with North Korean leader Kim Jong Un in Singapore, marking the first face-to-face talks between a sitting U.S. president and North Korean premier in history.

During the summit, the two leaders signed a brief document committing the U.S. to unspecified security guarantees for the North in exchange for Pyongyang agreeing to the eventual denuclearization of the Korean Peninsula.

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Trump touted the agreement as a major success, declaring a day after the meeting that North Korea is "no longer a nuclear threat."

But an NBC News report on Friday appeared to cast doubt on whether the North is actually committed to denuclearization, saying that U.S. intelligence officials believe that the country has increased fuel production for nuclear weapons at several secret research facilities.