U.S. President Barack Obama has chosen Mark Lippert, one of his closest aides, to be Washington's next ambassador to Seoul, multiple diplomatic sources here said Thursday.

The White House will soon announce the nomination of Lippert, Defense Secretary Chuck Hagel's chief of staff, to replace Sung Kim, who is nearing the end of a three-year stint in Seoul, the sources added. 

"The Obama administration earlier informed the South Korean government of the decision. South Korea has already given diplomatic consent," an informed source said. "President Barack Obama's visit to Seoul last week helped facilitate the traditional diplomatic process."

If confirmed, Lippert, 41, would become the youngest U.S. ambassador to South Korea. He would also be a rare non-career diplomat to take up the post.

Lippert is one of Obama's oldest and closest advisers on foreign policy. He erved in Obama's Senate office.

He is also known for his expertise on Korea and broader regional security issues, having worked as assistant secretary of defense for Asian and Pacific security affairs from April 2012 until May 2013.

He previously worked as chief of staff for the White House National Security Council (NSC).

South Korean officials welcomed Obama's choice.

"Mr. Lippert has a good reputation in the diplomatic circles here. He has lots of interest in Asia," a South Korean embassy official said.

Victor Cha, former director for Asian Affairs at the NSC, wrote in the Foreign Policy megazine that, "He is one of the most knowledgeable policy people on Asia in this administration and he is well-networked within the White House."

Every country wants an ambassador that can pick up the phone and get the president's attention and Lippert can do it, Cha added. (Yonhap)