Foreign Minister Makiko Tanaka, already under fire for making controversial remarks about the U.S. missile defense plan, has insinuated that Japan needs to depart from its decades-old security alliance with the United States, government sources said Tuesday.

The allegation came in the latest round of mudslinging between Foreign Ministry bureaucrats and Tanaka, who accuses ministry officials of waging a smear campaign by leaking to the media her comments with foreign diplomats.

Sources said that on May 25 in Beijing, Tanaka told Joschka Fischer, German vice chancellor and foreign minister, that the alliance was "an easy way" for Japan to enjoy security under the U.S. nuclear umbrella after World War II.