United States President Joe Biden and Britain’s new Prime Minister Rishi Sunak have agreed to work together to support Ukraine and stand up to China, the White House said in a statement, in a first phone call hours after Sunak became Britain’s third prime minister this year.

The two leaders reaffirmed the “special relationship” that exists between their countries and said they would work together to advance global security and prosperity, the White House said in a read-out of the conversation on Tuesday.

“The leaders agreed on the importance of working together to support Ukraine and hold Russia accountable for its aggression,” it said.

Biden and Sunak also agreed to “address the challenges posed by China,” which Washington has identified as its top geopolitical and economic rival on the world stage.

Downing Street released its own read-out of the call in which it said the pair “discussed the extent of UK-US cooperation, both bilaterally and in regions such as the Indo-Pacific,” as well as the more contentious issue of Northern Ireland.

The United States and the United Kingdom are the closest of allies. I look forward to working together with @POTUS to enhance stability across the world and continue our leading role in support of the people of Ukraine. 

Earlier on Tuesday Biden had congratulated Sunak in a tweet.

On Monday, he described the naming of Britain’s first non-white prime minister as “pretty astounding, a groundbreaking milestone”.

Sunak, the eldest son of a doctor and pharmacist of Indian descent, inherited an economic crisis after the resignation of Liz Truss after six weeks in office.

He held his first call with President Volodymyr Zelenskyy on Tuesday, in which he pledged the UK’s “steadfast support” for Ukraine.

Britain has been a key European ally of the United States in arming and supporting the Ukrainian military as it tries to repel the Russian invasion, which began last February.

Both his predecessors Boris Johnson and Truss had vocally promised full support to the war-torn country and on Tuesday evening the new prime minister said the UK’s support would be as “strong as ever” under his leadership.

Calling it a “privilege” to speak to Zelenskyy, who had earlier sent him congratulations, Sunak tweeted: “Both he and the Ukrainian people can count on the UK’s continued solidarity and support. We will always stand with Ukraine.” Zelenskyy, in a tweet, called it an “excellent conversation,” with the pair agreeing to “write a new chapter” in relations between the two countries.