U.S. Pacific Command chief Adm. Harry Harris, nominated to be ambassador to Canberra, will instead fill the long-vacant post of ambassador to South Korea, Australia's top diplomat said Wednesday.

Australian Foreign Minister Julie Bishop said she had been informed of the decision by acting U.S. Secretary of State John Sullivan on Tuesday.

"While we would have welcomed Adm. Harris here as ambassador to Australia, we understand that there are significant challenges for the United States on the Korean Peninsula," Bishop was quoted as saying.