TOKYO — The U.S. Embassy in Tokyo received several calls in February threatening to kill Ambassador Caroline Kennedy, investigative sources said March 17.

Tokyo police are investigating the calls, made by someone speaking English and in a male voice, as a suspected case of blackmail, according to the sources. An embassy official declined to comment.

Investigative sources said there have also been calls threatening to kill the U.S. Consul General in Naha, Okinawa Prefecture, Alfred Magleby.

Kennedy, the daughter of assassinated U.S. President John F. Kennedy, assumed the post of U.S. ambassador to Japan in 2013, while Magleby has been in his position since 2012.