Joe Biden opened a St Patrick's Day speech at the White House by saying: "I may be Irish, but I'm not stupid."
While some interpreted his remark as a self-deprecating joke, others suggested it could be seen as offensive to Ireland.
Mr Biden began his speech by saying: "Father, before I begin. Bless me, Father, for I’m about to sin. I, well, I just want you to know, I may be Irish, but I’m not stupid. I married Dominic Giacoppa’s daughter."
The joke was greeted with laughter in the room, and there was no reaction from Irish officials.
But some Republicans and social media commentators were critical.
Thomas Massie, a Republican congressman from Kentucky, said: "Is either of his assertions true?"
The Republican National Committee released a video of the comment on Twitter:
It was at least the third time Mr Biden has used the phrase.
He did so during the early stages of the 2020 presidential election campaign, speaking to an audience in Iowa.
At the time Trina Vargo, a former Obama adviser on Irish relations, said: "Joe Biden clearly has nostalgic feelings about his Irish ancestry, so I doubt he intended to insult Irish people. But that does not excuse such a comment.
"There remain dated and ignorant stereotypes of the Irish and it is time for Americans, including some Irish-Americans, to catch up with the times and have a more sophisticated understanding of the Irish."
In 2015, Mr Biden said the same thing to Lindsey Graham, the Republican senator, at a swearing-in ceremony for new senators.
Mr Biden reportedly positioned himself next to an attractive woman for a photograph and told Mr Graham: "I may be Irish, but I'm not stupid."
The US President has always been fiercely proud of his Irish heritage.
His great-great-grandfather arrived from Ireland to Scranton, Pennsylvania, in the mid-19th Century.
He made his latest remarks at the Annual Friends of Ireland Luncheon on Thursday.
Mr Biden told the event: "My grandfather, Ambrose Finnegan, used to say, and I mean this, he’d say, 'Joey, if you’re lucky enough to be Irish, you’re lucky enough.'"
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