SEOUL, South Korea — When President Moon Jae-in of South Korea sits down with President Trump and the Japanese prime minister, Shinzo Abe, in New York on Thursday, he will be meeting two of his strongest allies in pressuring North Korea over its nuclear and missile programs.

But Mr. Moon will also find himself a bit of the odd man out.

As the three leaders prepared for their trilateral summit meeting on the sidelines of the United Nations General Assembly meeting this week, the White House has struck an increasingly bellicose tone toward North Korea. Mr. Trump, addressing the General Assembly on Tuesday, said the United States would “totally destroy North Korea” if necessary.

On Wednesday, Mr. Abe defended the Trump administration’s approach, telling the General Assembly that for North Korea, “dialogue was the best means of deceiving us and buying time.”

Like Mr. Trump and Mr. Abe, Mr. Moon strongly advocates imposing sanctions and pressure on North Korea. But unlike them, he has repeatedly and categorically ruled out military action.