Pope Leo, the first US pontiff, has expressed “great love” for his home country and its core principles of freedom, opportunity and welcoming immigrants, but qualified that he “just happens to be American”.

In an interview with the US broadcaster NBC on the sidelines of a prayer event in Castel Gandolfo, the papal retreat near Rome, Leo, who has condemned the immigration policies of Donald Trump’s administration, spoke about his own family history in describing his relationship with the US.

He said his grandparents were immigrants while on his mother’s side, “we have people who were both slaves and slave owners”.

When asked how important being American was to him, Leo said: “I think of myself more as the pope who happens to be American. Not to belittle what it means to be an American.

“I have great love for America but I understand my mission as having a very important dimension, which is precisely being pastor of a universal church and having a voice and an opportunity to speak to people throughout the world.”

Asked what he loved about the US, he replied: “So many things. In a sense, speaking about principles, what America stands for, the sense of freedom, the sense of opportunity, the sense of having invited for generations people from around the world to be part of America.”

Having grown up in the US, Leo, who spent two decades as a missionary in Peru, said he continued to hold the principles “that have been a part of being American for so many years”.

Since being elected pontiff in May last year, Leo, 70, has repeatedly spoken up for migrants and called Trump’s immigration policies “inhuman”.

Relations with the Trump administration worsened further after the pontiff strongly condemned the US-Israeli war against Iran.

In his first key address to the US on the eve of the 250th anniversary of the signing of the Declaration of Independence, he praised the country’s history of welcoming migrants while urging Americans to live up to the ideals put forward in the declaration, in what was seen as another rebuke to Trump.

The pontiff marked 4 July with a brief visit to the southern Italian island of Lampedusa, one of the main entry points to Europe for people making the perilous sea crossing from north Africa in search of refuge.

Leo is yet to take up Trump’s invitation to the White House, made by the vice-president, JD Vance, during a meeting at the Vatican the day after his inaugural papal mass. Leo told NBC that no trip had been planned, but he hoped to visit the US soon.