WASHINGTON, Sept 7 ― President Joe Biden spoke by phone yesterday to Liz Truss to congratulate her on becoming Britain's new prime minister and both leaders vowed to strengthen their relationship as they stand together against Russia.

"I look forward to deepening the special relationship between our countries and working in close cooperation on global challenges, including continued support for Ukraine as it defends itself against Russian aggression,” Biden said in a tweet.

The two leaders spoke by phone yesterday afternoon, and could meet as soon as the UN General Assembly later in September.

The prime minister's office said in a statement they discussed deepening cooperation on Nato and the US-Australia-Britain security agreement set up last year as a counter to China.

Truss looks forward to "working closely with President Biden as leaders of free democracies to tackle shared challenges, particularly the extreme economic problems unleashed by Putin’s war,” the British statement said.

Truss won a leadership race for the governing Conservative Party on Monday and took over as prime minister on Tuesday, as Britain faces its most daunting set of challenges in decades.

The so-called special relationship between the United States and Britain has maintained solid continuity in recent years, despite frictions between then-President Donald Trump and then-Prime Minister Theresa May.

Washington and London have been aligned on helping Ukraine in its war against Russia and in countering China's influence in the Pacific. But a bilateral trade deal that some British officials hoped could offset trade and economic upheaval after Brexit has yet to materialise under Biden.

A US official said the White House expects a lot of continuity from Boris Johnson to Truss and that Biden and Truss are likely to be aligned on countering Russia’s invasion in Ukraine and China’s rising influence in the Indo-Pacific.

Biden got on well with Johnson, but he could have tensions with Truss over Northern Ireland.

As a member of parliament, she introduced legislation to undo the Northern Ireland Protocol, and Biden has been insistent that Britain do nothing that could endanger a quarter century of peace in Northern Ireland.

The British statement on the phone call said both leaders "agreed on the importance of protecting the Belfast (Good Friday) Agreement.” US State Department deputy spokesperson Vedant Patel reiterated the US position on the Northern Ireland peace accord yesterday.

The "US priority remains protecting the gains of the Belfast Good Friday Agreement and preserving peace and stability and prosperity for the people of Northern Ireland,” he said. ― Reuters