"Congratulations on your appointment as Prime Minister Giorgia Meloni," Stoltenberg tweeted.

"Italy is a founding member of NATO, committed to the transatlantic bond and making strong contributions to our security in a more dangerous world. I look forward to working with you."

Meloni, the 45-year-old leader of the post-fascist Brothers of Italy party, took office on Saturday, promising to keep her country "fully, and with its head held high, part of Europe and the Atlantic Alliance (NATO)".

That pledge contrasted with the stances of her partners in her coalition government, who are both considered close to Russia.

One of them is Matteo Salvini, a long-time fan of President Vladimir Putin, who is now deputy prime minister under Meloni.

The other is former premier Silvio Berlusconi, who was this week heard in a leaked recording talking about his warm ties with Moscow and appearing to blame Russia's war in Ukraine on President Volodymyr Zelensky.

Meloni, in a tweet on Saturday thanking Zelensky for his congratulations to her, said: "Italy is and will always be on the side of the brave people of Ukraine that is fighting for its freedom and for a rightful peace."