(CNN) Japanese authorities are investigating death threats against the American ambassador to Japan, Caroline Kennedy, according to Japanese media reports and international wire services.

Local police are looking into phone calls placed last month to the U.S. Embassy in Tokyo threatening to kill Kennedy, according to local media reports. CNN could not immediately confirm the reports.

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"We take any threats to U.S. diplomats seriously," said State Department deputy spokesperson Marie Harf. "We take every step possible to protect our personnel. We are working with the Japanese government to ensure the necessary measures are in place. We will not comment on the specific details of any threats or the steps we take to address them."

News of the threats come two weeks after the Mark Lippert , the American ambassador to South Korea, was slashed by an assailant wielding a 10-inch knife at an event in Seoul. Lippert is recovering from gashes to his face and wrist.

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