The Foreign Ministry erased the description that South Korea shares "fundamental values" with Japan from this year's diplomatic policy report to criticize its prosecution of a Sankei Shimbun journalist, according to a senior member of the Liberal Democratic Party.

Tatsuya Kato, former Seoul bureau chief for the Sankei Shimbun, is being tried on charges of defaming South Korean President Park Geun-hye and has been banned from leaving South Korea since last August.

In an article published online, Kato questioned Park's whereabouts during the Sewol ferry disaster last April that killed more than 300 people.

"It's unthinkable from the viewpoint of (protecting) freedom of speech," Takeo Kawamura, secretary-general of a parliamentary group to promote ties with South Korea, told BS Fuji TV on Tuesday. "You can take it as a message that South Korea is not mature enough."

The case has added to already soured relations between the two countries amid the ongoing dispute over the South Korean-controlled Takeshima islets in the Sea of Japan that Japan considers its sovereign territory. South Koreans call the pair of outcroppings Dokdo.

In last year's Diplomatic Bluebook, the Foreign Ministry refers to South Korea as the "most important neighboring country with which Japan shares fundamental values such as freedom, democracy and basic human rights as well as interests such as securing regional peace and stability."

This year, however, it only described South Korea as "the most important neighboring country."

Kawamura also criticized Seoul for its decision to join the Asian Infrastructure Investment Bank, a China-led initiative that Japan is reluctant to join.

"My feeling is that it's out of place in the relationship between Japan, the U.S. and South Korea," he said of Seoul's decision. "It's the kind of issue that calls for consultation between Japan and South Korea."