Liz Truss on Tuesday formally became the new UK prime minister after being appointed by Queen Elizabeth II during an audience at her Balmoral estate in Scotland.

Royal officials released a picture of the monarch and Truss shaking hands to formalise her appointment, after Boris Johnson earlier tendered his resignation.

"The Queen received in Audience The Right Honourable Elizabeth Truss MP today and requested her to form a new Administration," a Buckingham Palace statement said.

"Ms Truss accepted Her Majesty's offer and kissed hands upon her appointment as Prime Minister and First Lord of the Treasury." (Agencies)