The top bureaucrat at the Foreign Ministry on Friday rebutted China's justification that one of its naval vessels was exercising the right to free passage through an international strait when it sailed in and around Japanese territorial waters earlier this month.

"(The area) is in our country's territorial waters. In light of the actual usage, it cannot be called an international strait" as China claims, Vice Foreign Minister Shinsuke Sugiyama, who assumed the post on June 14, said in an interview.

On Chinese military vessels' recent assertiveness at sea, Sugiyama said, "Circumstances are different in each case but, as a whole, it's extremely undesirable. I have serious concern about China's growing military activities."