US President Donald Trump’s national security adviser Robert O’Brien says he will ensure a professional transition to the team led by Democrat Joe Biden if Biden is deemed the winner of the 2020 presidential election and “obviously things look like that now”.

The Republican Trump has insisted the November 3 election was “rigged” and that he will be declared the winner after a series of legal challenges in several US states.

Speaking to the Global Security Forum, Mr O’Brien said that while he hoped Mr Trump would turn out to have won a second four-year term, he would work with a new administration headed by Mr Biden and his vice presidential running mate Kamala Harris.

“If there is a new administration, look, they deserve some time to come in and implement their policies,” Mr O’Brien said.

“If the Biden-Harris ticket is determined to be the winner – obviously things look that way now – we’ll have a very professional transition from the National Security Council, there’s no question about it.”

Mr Trump’s campaign has so far failed to produce evidence that could overturn Mr Biden’s 306-232 victory in the state-by-state Electoral College vote.

States face a December 8 “safe harbour” deadline to certify their elections and choose electors who will officially select the new president on December 14.

Mr O’Brien said it appeared Mr Biden was prepared to bring in a professional national security team.

“The great thing is this is the United States of America,” the national security adviser said.

“We pass the baton and have had peaceful, successful transitions even in the most contentious periods.”

-AAP