Donald Trump
Trump is considering his VP pickIsaac Brekken/Getty

An outspoken military chief, who previously worked for Barack Obama, is rumoured to be on the shortlist as Donald Trump's VP running mate.

Lt. Gen. Michael Flynn, the retired chief of the Defense Intelligence Agency – who was critical of the Obama administration's policy on terrorism – has spoken with Trump's team several times during the campaign.

However, he did not comment on whether he was playing a larger role than occasional adviser to the candidate, and refused to comment on whether Trump's campaign had contacted him about a VP role.

"One of the things I expect Mr. Trump would look for in a vice president is discretion," Flynn told the New York Post.

"All I would say is that I have been honoured to serve my country for the past three decades and look forward to serving in other ways now that I am retired from the US Army. I've been a soldier too long to refuse to entertain any request from a potential commander in chief."

Trump has been tweeting his search for a running mate, telling his followers he had met with Indiana governor Mike Pence and Iowa senator Joni Ernst, both of whom are reportedly shortlisted. They join former presidential hopeful Chris Christie, and former House Speaker Newt Gingrich, who is a favourite to take the post.

According to Trump, people are vying to be his running mate: "The only people who are not interested in being the V.P. pick are the people who have not been asked!"

A definite choice for VP is expected to be announced at the Republican National Convention in Cleveland, Ohio, from 18-21 July, when Trump is also set to be officially selected as the party's candidate.