It was not the first linguistic gaffe by an American official in the Trump era. Ahead of a meeting between Mr. Trump and President Xi Jinping of China in Germany last year, for example, a White House statement referred to Mr. Xi as the leader of the Republic of China — the formal name for Taiwan, which China considers part of its territory. Another called Shinzo Abe, the prime minister of Japan, the country’s “president.”

Mr. Pompeo is new to the State Department, but his mistake was surprising in part because he is a former director of the Central Intelligence Agency, and someone who has dealt extensively with North Korea. Some observers said on social media that the slipup — which came on the same day that Mr. Kim was visiting China — was an insult that showed a lack of United States preparation for the planned Trump-Kim summit meeting.

“The Kimness of the Kim regime seems pretty well established,” John Delury, an expert on China and the Koreas at Yonsei University in Seoul, South Korea’s capital, said with a laugh in a telephone interview. He raised the possibility that the mistake could have been because of a State Department transcription error.

Still, Mr. Delury added, it was easy to see how an outsider could become confused about a North Korean name. Unlike South Koreans, North Koreans typically do not hyphenate their given names in English translations, he said. The South Korean president’s name is spelled Moon Jae-in, for example, whereas North Koreans typically write “Kim Jong Un” — three distinct names, without a hyphen.