US President Donald Trump has arrived in Rome for the funeral of Pope Francis, where he will brush shoulders with an array of world leaders on the unexpected first foreign trip of his second term.

Trump, accompanied by wife Melania, had a distant relationship with the late pontiff who criticized him sharply on his signature policy of mass deportations of migrants.

But Trump will be centre-stage for a major diplomatic gathering on Saturday with some 50 heads of state, including 10 reigning monarchs, at the Vatican.

Trump said it was possible he could meet Ukrainian President Volodymyr Zelensky in what would be the two leaders' first time together since a disastrous White House meeting on February 28.

Trump and Vice President JD Vance in that meeting berated Zelensky, calling him ungrateful for the billions of dollars of US military assistance given since Russia invaded Ukraine in 2022.

Trump, while calling on Russia to stop its aerial attacks on Ukraine, has recently blamed Zelensky for the war and the continuing bloodshed.

Zelensky said he may miss the funeral however due to military meetings after a deadly Russian strike on Kyiv.

No meetings have been announced in Rome for Trump, who is due to stay only half a day.

Trump said on Air Force One he would meet "some people" including Italian Prime Minister Giorgia Meloni, whom he hosted this month to discuss tariffs.

But he said any meetings would be quick and added: "Frankly it's a little disrespectful to have meetings when you're at the funeral of the pope."

Trump may also find discomfort around some of the other mourners – chief among them his predecessor, Joe Biden.

Biden is a devout Catholic and was close with Francis. He will travel independently to Rome, his office said, even though former presidents generally travel on Air Force One for funerals.

Trump's trip to Italy comes after he rattled European allies by imposing sweeping tariffs, although he at least temporarily has backed down from the most severe measures.

French President Emmanuel Macron, one leader who has managed to forge a bond with Trump, and outgoing German Chancellor Olaf Scholz will be at the funeral, as will top EU officials Ursula von der Leyen and Antonio Costa.

Trump will however be keeping one important appointment: with First Lady Melania Trump for her 55th birthday, which also falls on Saturday.

He said he hadn't had time to buy any presents but added that "I'm taking her for dinner on Air Force One." (AFP)