"When I left Conference Room for short meetings with Japan and other countries, I asked Ivanka to hold seat. Very standard. Angela M agrees!" he tweeted.
"If Chelsea Clinton were asked to hold the seat for her mother, as her mother gave our country away, the Fake News would say CHELSEA FOR PRES!" he added
Clinton quickly responded
on Twitter: "Good morning Mr. President. It would never have occurred to my mother or my father to ask me. Were you giving our country away? Hoping not."
Ivanka Trump has not yet commented about the incident.
When Ivanka Trump sat in on behalf of her father during a working session on Saturday morning in Hamburg, Germany, her presence caused a stir among Trump critics on social media.
A photo of the first daughter sitting next to Chinese President Xi Jinping, British Prime Minister Theresa May, Turkey's Recep Tayyip Erdogan and German Chancellor Angela Merkel was first tweeted by Svetlana Lukash, who identifies herself on Twitter as a G20 Russian sherpa, a title given to people who help international delegations at large summits. The tweet has since been deleted.
It is uncommon for a member of a first family to sit in on a meeting of this level with world leaders, but Ivanka Trump serves the administration in a formal capacity as an adviser to the President.
A senior Trump administration official confirmed that Ivanka Trump had stepped in for her father, but dismissed any suggestion it was improper or unusual.
"Ivanka was sitting in the back and then briefly joined the main table when the President had to step out and the President of the World Bank started talking as the topic involved areas such as African development -- areas that will benefit from the facility just announced by the World Bank," the senior administration official told CNN.
"When other leaders stepped out, their seats were also briefly filled by others," the official noted.
Merkel said Saturday that her presence was not uncommon.
"The delegations themselves decide" who will sit in for a President if they can't be present for a meeting, Merkel told reporters.
"Ivanka Trump was part of the American delegation, so that is something that other delegations also do, and it is very well known that she works in the White House and that she is also engaged in certain initiatives," Merkel said.
But Michael McFaul, the United States ambassador to Russia under President Barack Obama, said Ivanka Trump subbing in was unusual.
"This is strange," he tweeted
. "Very strange."
And Brian Fallon, a CNN political commentator and former spokesman for Hillary Clinton's presidential campaign, tweeted
, "I'm sure Republicans would have taken it in stride if Chelsea Clinton was deputized to perform head of state duties."
Merkel and Ivanka Trump have worked together on a series of issues. Trump first traveled to Germany at Merkel's invitation in April for the Women 20 Summit, and worked at the G20 summit with Merkel and World Bank President Jim Yong Kim to roll out a new initiative
aimed at promoting women's entrepreneurship in developing countries.