A prominent ally of Donald Trump has urged him to drop his efforts to overturn his loss to Joe Biden in the US presidential election.

Former New Jersey Governor Chris Christie called the president’s legal team a “national embarrassment”.

President Trump has refused to concede the election, making unsubstantiated claims of widespread electoral fraud.

Many Republicans have supported his legal efforts, although a small but growing number have broken ranks.

Voting in the US election ended on 3 November. Mr Biden is projected to beat President Trump by 306 votes to 232 in the US electoral college when it meets to formally confirm the winner on 14 December. This is far above the 270 votes he needs.