“Dolphin fishing is a form of traditional fishing in our country,” he said, responding to a question about Ms. Kennedy’s criticism. “We will explain Japan’s position to the American side.”

Ms. Kennedy’s decision to wade into the issue came as something of a surprise and could carry extra weight, given her prominence. She took up the post in November, becoming the first woman to serve as ambassador to Japan, and her appointment was seen as particularly significant, given her close ties to President Obama. He benefited from her high-profile endorsement during the 2008 campaign, which gave his candidacy an important early blessing from a leading member of the Kennedy clan.

Ms. Kennedy’s remarks came just a month after the United States Embassy in Tokyo expressed its “disappointment” with the decision of the Japanese prime minister, Shinzo Abe, to visit the Yasukuni Shrine, which honors the nation’s war dead, including war criminals who were executed after Japan’s defeat. The visit angered China and South Korea, which suffered greatly under Japanese aggression during the first half of the 20th century.

After the shrine visit, Japan’s foreign minister, Fumio Kishida, called Ms. Kennedy during her vacation to explain Mr. Abe’s reasoning for making the visit.

The practice of drive hunt killing of dolphins has come under increasing criticism, particularly since the 2009 release of the documentary “The Cove,” which won the 2010 Academy Award for best documentary. The movie included graphic scenes of the annual dolphin hunt in Taiji, Japan, which is underway now and has ignited the latest flurry of criticism of the practice.