Japanese police on Thursday arrested a man for making threatening phone calls to the US embassy including against ambassador Caroline Kennedy, U.S. officials said.
Kennedy, the last surviving child of the assassinated U.S. president John F. Kennedy, took up her post in Tokyo in November 2013 as the first woman U.S. ambassador to the Asian nation.
It emerged Wednesday that U.S. and Japanese officials were investigating death threats made against her several weeks ago.
"We are working and have been working for several weeks with the Japanese government on these reports, these threats," State Department spokeswoman Jen Psaki told reporters.
"The Japanese police arrested a 52-year-old individual from Okinawa for making threatening phone calls against the embassy... not just related to the ambassador," Psaki said.
The arrest was "a positive step," she said, adding the State Department would stay in close touch with Japanese authorities.
According to Japanese media, the caller had also threatened to kill the U.S. consul general in Okinawa, Alfred Magleby.
The news of the threats came only weeks after the U.S. ambassador to South Korea, Mark Lippert, was stabbed and injured during a public event in Seoul.
Lippert had to have 80 stitches to his face and was hospitalized for five days after being attacked by a knife-wielding nationalist during a breakfast event in the South Korean capital.
Psaki stressed there was no connection between the attack on Lippert and the threats against Kennedy.