Donald Trump has said he will issue an executive order to mandate identification for all US elections, a move likely to be challenged in court as unconstitutional.

"Voter I.D. Must Be Part of Every Single Vote. NO EXCEPTIONS! I Will Be Doing An Executive Order To That End!!!,” the US president said on Truth Social late on Saturday.

Trump also claimed he wants to ban all voting by mail except for those who are very ill or in military service.

The US constitution grants primary authority to regulate elections to the US states, while empowering Congress to enact election laws or regulations. It gives no explicit authority to the president to regulate voting.