hina said on Monday that its naval ship conducted a “lawful and legitimate” transit in Japan’s territorial waters last week, exercising its right under an international treaty on maritime law.

The Hai Yang 25, a Chinese hydrographic survey ship, entered Japan’s southwestern territorial waters in the Osumi archipelago from 6 a.m. to 7:53 a.m. on Saturday, according to the defense ministry in Japan. The ship is used to conduct research on underwater topography for submarine navigation.

“The Tokara Strait can be sured for international navigation, and by sailing through the strait, the Chinese vessel was exercising its right of transit passage, which is fully lawful and legitimate,” said Mao Ning, spokesperson for China’s Foreign Ministry, during a press conference on Monday.