New Prime Minister Rishi Sunak on Tuesday told Ukrainian President Volodymyr Zelensky he had Britain's "steadfast support", Downing Street said, in his first call with a foreign leader since taking power hours earlier.

"The Prime Minister said the United Kingdom's support for Ukraine would be as strong as ever under his premiership, and President Zelensky could count on his Government to stand in continued solidarity," a Sunak spokeswoman said.