US President-elect Donald Trump has offered the post of secretary of the interior to Montana congressman Ryan Zinke, according to reports. However, while Zinke has received the offer, it is not yet known where he will accept the position.

Sources close to the transition have told Politico that Zinke, who is also being considered as a Senate contender in 2018, is not showing whether or not he plans to take the nomination.

Zinke is a former Navy Seal commander who campaigned with Trump and was an early supporter of the candidate. He was believed to be in contention for the post alongside Cathy McMorris Rodgers and Raul Labrador, both representatives in Congress.

He is noted as a outdoorsman although he often votes against environmentalist lines when it comes to fossil fuel extraction.

One official announcement on Tuesday was the appointment of Stephen Miller as a senior policy adviser to Trump. Miller was previously an adviser to Trump's pick for attorney general, Jeff Sessions.

Miller has been a policy director in the transition team and was the chief speech writer during Trump's campaign.

"Stephen played a central and wide-ranging role in our primary and general election campaign," said President-Elect Trump. "He is deeply committed to the America First agenda, and understands the policies and actions necessary to put that agenda into effect.

"He is a strong advocate for protecting American workers, and will fulfill a crucial role in my administration as my senior advisor on matters of policy."

If Zinke accepts, he will join this week's two earlier nominations of Exxon Mobil CEO, Rex Tillerson, as secretary of state and former Texas governor Rick Perry as energy secretary. Both have quickly come under fire, with many criticising Tillerson's links to Russia and pointing out that Perry once infamously said he wanted to scrap the department of energy that he has now been nominated to head.