Washington: US President Donald Trump offered Senator Bob Corker the chance to be the US ambassador to Australia, but the Republican lawmaker, currently chairman of the Senate Foreign Relations Committee, said on Monday he turned the position down.

"At the end of the day, I just felt like it wasn't the right fit and I still had work to do in the Senate," Corker said in a telephone interview.

The United States has not had an ambassador in Australia since September 2016. Australia is an important US partner on issues ranging from China's military expansionism and North Korea's nuclear program to the conflicts in Syria and Afghanistan and the absence of such a high-profile representative has been felt in foreign policy circles.

Trump in February picked US Pacific Commander Admiral Harry Harris to be his top diplomat in Canberra, but instead nominated Harris this month to be ambassador to South Korea, another long-vacant post.

Corker, 65, has announced his intention to retire from the Senate when his second six-year term ends in December.