(Reuters) - American and Japanese authorities are working to ensure the safety of U.S. personnel in Japan after media reports of death threats against U.S. Ambassador Caroline Kennedy and another American diplomat, the U.S. State Department said on Wednesday.
The U.S. Embassy in Tokyo received the threats by telephone last month, with several phone calls made by an English-speaking man, the Yomiuri Shimbun newspaper reported, citing a Tokyo police official.
The threats also targeted the U.S. consul general in Okinawa, Alfred Magleby, according to Yomiuri and other Japanese and U.S. media reports. Okinawa island is known in Japan as host to the bulk of U.S. service personnel stationed in the country.
State Department spokeswoman Jen Psaki did not confirm any specific threats to Kennedy and Magleby, but she said in a statement, "We take any threats to U.S. diplomats seriously."
"We are working with the Japanese government to ensure the necessary measures are in place," she said.
The U.S. Embassy and Tokyo Metropolitan Police Department declined to comment.
Reports of the threats emerged as first lady Michelle Obama arrived in Japan on Wednesday for a three-day visit, including a meeting with diplomatic staff from Tokyo and Osaka.
The reports came two weeks after the U.S. ambassador to South Korea, Mark Lippert, was attacked and injured by a man with a knife during an event in Seoul.
That prompted debate about threats against American diplomats abroad and the precautions taken to protect U.S. ambassadors. The State Department has said security for Lippert was adequate.
Security for U.S. ambassadors worldwide is based on assessments by experts from the State Department's Bureau of Diplomatic Security, according to the department.
Lippert had been assigned a single South Korean National Police bodyguard but his security was increased after the attack to include several other police officers, the State Department has said.
Earlier this month, department spokeswoman Marie Harf said she was not aware of plans to boost diplomatic security elsewhere in the world following the attack.
It was not clear what security arrangements have been provided for Kennedy, the daughter of former U.S. President John F. Kennedy. She began her assignment in Japan in November 2013.
Authorities probe threats against Caroline Kennedy in Japan -reports
NEW YORK, UNITED STATES: US First Lady and New York Democratic senate candidate Hillary Rodham Clinton (R) chats with Caroline Kennedy Schlossberg (L) at a New York Women for Hillary event in New York 17 October 2000. Clinton will continue campaigning with Caroline Kennedy 17 October 2000 and join US Senator Ted Kennedy (D-MA) for an event in Buffalo, New York. (FILM) AFP PHOTO/Doug KANTER (Photo credit should read DOUG KANTER/AFP/Getty Images)
Caroline Kennedy responds during an interview, Friday, Dec. 26, 2008 in New York. Ms. Kennedy is one of the candidates in the running to replace Senator Hillary Clinton (D-N.Y.) after Clinton is confirmed as Secretary of State in President-Elect Obama's administration. (AP Photo/Stephen Chernin)
Caroline Kennedy listens to a reporter's question during a news conference at City Hall in Buffalo, N.Y. on Wednesday, Dec. 17, 2008. Caroline Kennedy finally made public her desire to carry on her famous family's legacy, reaching out to a handful of political leaders Wednesday in an effort to win support for her quest to succeed Hillary Rodham Clinton in the U.S. Senate. (AP Photo/Don Heupel)
**FILE**In the Oct. 15, 2008 file photo, Caroline Kennedy sits with husband, Edwin Schlossberg before the start of the a presidential debate at Hofstra University in Hempstead, N.Y. After warily stepping into the political free-for-all for Hillary Rodham Clinton's U.S. Senate seat, Kennedy's holiday activities include fending off requests to disclose financial and other personal information. (AP Photo/J. Scott Applewhite, File)
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Former US Secretary of State Hillary Clinton speaks after receiving the 2013 Lantos Human Rights Prize during a ceremony on Capitol Hill in Washington on December 6, 2013. AFP PHOTO/Nicholas KAMM (Photo credit should read NICHOLAS KAMM/AFP/Getty Images)
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