WASHINGTON (REUTERS) - Japanese police have arrested a man in connection with telephone threats made to the US Embassy and American Ambassador Caroline Kennedy, the State Department said on Thursday.

State Department spokeswoman Jen Psaki said a 52-year-old man from Okinawa was apprehended by police in Japan but did not provide further details.

"We take any threats very seriously - we have been working for weeks with the Japanese government," she said.

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 US ambassador to South Korea, Mark Lippert, was injured by a man with a knife.

Psaki said the threats in Japan began before Lippert was attacked and the events were not connected, Psaki said.