President Trump's previously undisclosed conversation with Russian President Vladimir Putin occurred because first lady Melania Trump had been assigned a seat beside Putin at an official dinner during the G-20 summit in Hamburg earlier this month, a White House official said Tuesday evening.

"Chancellor Merkel hosted a dinner for leaders and spouses only, and the German government set the seating arrangements," the official said after reports of a second meeting between Trump and Putin surfaced on Tuesday. "The concert [earlier that evening] and dinner were publicly announced on both the president's schedule and the G-20 schedule, with the clear understanding that all visiting leaders would be present."

"At the dinner, President Trump was seated between Mrs. Abe, wife of the Prime Minister of Japan, and Mrs. Macri, wife of the President of Argentina. Mrs. Trump was seated next to President Putin," the official explained. "During the course of the dinner, all the leaders circulated throughout the room and spoke with one another freely. President Trump spoke with many leaders during the course of the evening. As the dinner was concluding, President Trump went over to Mrs. Trump, where he spoke briefly with President Putin."

Critics quickly seized on news of the meeting Tuesday, questioning why the White House did not disclose it on the day of the summit. Trump and Putin had a high-profile bilateral meeting on the morning of July 7, and the encounter was characterized at the time as their only formal contact during the G-20.

But the White House pushed back forcefully on the suggestion that officials had sought to conceal a conversation between Trump and Putin.

"There was no 'second meeting' between President Trump and President Putin, just a brief conversation at the end of a dinner. The insinuation that the White House has tried to 'hide' a second meeting is false, malicious and absurd," a White House official said. "It is not merely perfectly normal, it is part of a president's duties, to interact with world leaders. Throughout the G20 and in all his other foreign engagements, President Trump has demonstrated American leadership by representing our interests and values on the world stage."

The White House noted that Trump and Putin relied on the Russian translator because the translator who accompanied Trump spoke only Japanese.

Trump's informal conversation with Putin came to light thanks to Ian Bremmer, president of Eurasia Group, who described the meeting in a company newsletter on Tuesday and then again in an interview on Bloomberg TV.