Ms. Trump, who had been sitting in the back during a session at the Group of 20 summit meeting, momentarily joined the main table when President Trump stepped out.
Ivanka Trump briefly sat in for her father, President Trump, during a session on Saturday at the Group of 20 summit meeting in Hamburg, Germany, prompting an outcry on social media and a swift defense from her brother Donald Trump Jr.
Ms. Trump, who had been sitting in the back of the room during a discussion of topics that were relevant to her, joined the main table when Mr. Trump had to step out, a White House official said.
When other leaders left the table, their seats were also filled by others in their delegations, the official added.
But Ms. Trump’s appearance riled the president’s critics, who have questioned the role that Mr. Trump’s family members play in the administration. Ms. Trump serves as a senior adviser to the president. Her husband, Jared Kushner, is also a senior adviser and the head of the new Office of American Innovation.
While Mr. Trump was away from the table, his daughter sat between President Xi Jinping of China and Prime Minister Theresa May of Britain.
A Russian official, Svetlana Lukash, captured the moment in a photograph and posted it on Twitter. Though she later deleted the tweet, the image lived on in a screenshot that riled up some on both sides of the aisle.
Representative Ted Lieu, Democrat of California, who serves on the House Foreign Affairs Committee, said on Twitter that based on Ms. Trump’s example, he was going to ask the House speaker, Paul D. Ryan, “if my son can sit in for me at the next House Foreign Affairs Committee meeting.”
Donald Jr. waded into the fray on Twitter after Ana Navarro, a Republican strategist and a frequent critic of President Trump, said she would prefer Ms. Trump as president.
“She is VERY smart & eloquent, ” Donald Jr. said of his sister in a response on Twitter . “You can belittle her all you want w your snark, but we all know 1 on 1 she way out of your league.”
Then he added: “If the left is so ‘outraged’ about Ivanka sitting in for a few minutes, maybe they’ d be happier if I sub in for a while?”
Chancellor Angela Merkel of Germany seemed to defend Ms. Trump’s appearance in comments after the session.
“The delegations themselves decide, should the president not be present for a meeting, who will take the chair, and Ivanka Trump was part of the American delegation, ” she told reporters. “It is very well known that she works at the White House and that she is engaged in certain initiatives.”
Ms. Trump’s move to the main table came hours after she joined Jim Yong Kim, the president of the World Bank, to introduce the Women Entrepreneurs Finance Initiative, which aims to help women access loans and start businesses in developing countries.
President Trump announced that the United States pledged $50 million to the initiative.
“I’ m very proud of my daughter Ivanka, always have been from day one, ” he said.
