US President Donald Trump and his administration are yet to find a suitable candidate to fill the longstanding vacancy for US ambassador to Australia despite working “assiduously” to recruit one, according to a senior US State Department official.

The key role has not been filled for almost two years.

The State Department official said on Thursday he did not believe a breakthrough announcement on the vacancy would be made at next week’s Australia-US Ministerial or AUSMIN consultations in California, where Foreign Minister Julie Bishop and Defence Minister Marise Payne will meet with US Secretary of State Mike Pompeo and Defense Secretary Jim Mattis.

“I don’t believe there will be an announcement,” the official, who asked not to be identified, told reporters on Thursday during a briefing ahead of AUSMIN.

“I am not aware there will be an announcement.

“What I can assure you is that the White House and the Department of State are working very assiduously on identifying an appropriate candidate for that position and it is one of the top positions the administration is focused on making sure we have the best candidate possible to fill that post as soon as possible.”

Recently retired Pacific Command commander Admiral Harry Harris had been announced as Mr Trump’s pick for the Canberra posting but in April, he was switched to the vacant South Korean ambassador role.

Senior Republican congressmen Orrin Hatch and Bob Corker have reportedly been asked, but both declined the Australian job.

AUSMIN, an annual meeting of Australian and US foreign and defence ministers, will be held at Stanford University, near San Francisco, on Monday and Tuesday.

The official said free and fair reciprocal trade and high-standard principle infrastructure in the Asia-Pacific, the ongoing denuclearisation talks with North Korea, and ongoing issues with China will also be on the agenda.

-AAP