Government officials must refrain from making comments suggesting Japan is willing to compromise in territorial negotiations and instead demand that Moscow return all four Russian-held islets off Hokkaido, a group of conservative professors and former diplomats said Thursday in Tokyo.

"A single careless comment can undo past efforts overnight," the group, led by Kenichi Ito of Japan International Forum, said in a statement critical of former Vice Foreign Minister Shotaro Yachi. It was reported in early April that Yachi said Tokyo could settle for a partial return of Kunashiri, Etorofu and Shikotan islands and the Habomai islets.

The group said it will publish the statement in newspapers on May 11 — the day Russian Prime Minister Vladimir Putin is slated to visit Japan.