British Prime Minister Rishi Sunak promised his Ukrainian counterpart Volodymyr Zelenskiy on a call that the UK's support for Ukraine would be steadfast and "as strong as ever under his premiership," a Downing Street spokesperson said.

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

Sunak took office earlier on Tuesday.

"Both leaders agreed on the need to continue to place pressure on Putin’s barbaric regime through continued economic sanctions ... (Sunak) said he hoped they would see each other in person soon," the spokesperson said. (Reporting by Muvija M, editing by Deepa Babington)