US President Joe Biden talked to Britain'snewly appointed Prime Minister Rishi Sunak on Tuesday and reaffirmed the "special relationship" between two nations.

Biden told the British PM in a phone call that the "UK remains America's closest ally."

The 42-year-old Sunak was officially appointed the prime minister of Britain after meeting King Charles at Buckingham Palace. He is taking over an economy in crisis amid political turmoil after the 49-day stint of his predecessor Liz Truss.

Ukraine and China discussed

According to a statement released by the White House, the two leaders discussed Russia's invasion of Ukraine and "agreed on the importance of working together to support Ukraine and hold Russia accountable for its aggression."

Sunak and Biden also discussed the means to "address the challenges posed by China." As geopolitical and economic adversaries, Beijing and Washington see each other as rivals.

The two leaders also talked about the issue of Northern Ireland and their commitment to the Good Friday Agreement.

The nomination of Sunak as Britain's first non-white prime minister was described as "pretty astounding, a groundbreaking milestone" by the US president on Monday.

Biden and Meloni talk by phone too

Separately, President Biden spoke by phone on Tuesday to Giorgia Meloni, who was recently appointed Italy's Prime Minister. The pair discussed their commitment to continue providing assistance to Ukraine, the White House said.

The Meloni administration is Italy's most right-wing government since World War II. Former close ties between Russia and two of her coalition partners have also raised concerns with NATO allies.

Meanwhile, Meloni said that she was willing to work with Britain's Sunak and his administration over their "shared values of freedom and democracy."