South Korea's new ambassador to the United States Lee Soo-hyuck arrived in Washington on Thursday, his office said, as the allies face a series of difficult issues, including North Korea and defense cost-sharing.

His inauguration ceremony will be held at the South Korean Embassy in Washington on Friday, and Lee is soon expected to present his credentials to US President Donald Trump, according to the embassy.

He was named the top envoy to the US by President Moon Jae-in in August and was formally appointed last week following US consent early this month.

Part of his first official schedule as ambassador will include a visit the memorial cemetery in Washington to pay tribute to late American veterans who fought in the 1950-53 Korean War. He then plans to meet with State Department officials and members of the Korea Caucus in Congress.

Lee, a retired career diplomat, is tasked with a big job as Seoul and Washington are facing a number of bilateral and

trilateral regional security issues, including the ongoing defense cost-sharing talks with Washington and a row with Tokyo over history and trade that led to Seoul's decision to terminate a military information-sharing pact with Tokyo.

Before departing for Washington, Lee told reporters in Seoul that he would seek to encourage Washington to play "a constructive role" in resolving tensions between Seoul and Tokyo.

Lee was South Korea's first chief nuclear negotiator for the six-party talks involving the two Koreas, the US, China, Japan and Russia when it was launched in 2003 with the goal of resolving the North Korean nuclear issue. (Yonhap)