The Chinese Coast Guard sailed three ships within Japan’s territorial waters yesterday, likely another intentional provocation fitting a pattern of recent Chinese actions in the South China Sea.

The territorial waters in question are part of the Senkaku Islands, a handful of uninhabited islands that lay roughly due east of Mainland China. Japan has claimed ownership of the islands since the late 19th century.

China, who refers to the islands as the Diaoyu Islands also claims them as Chinese territory.

Of particular note is the timing of just such an action near the Senkakus. During his recent visit to Japan, Defense Secretary James Mattis specifically addressed Japanese sovereignty over the islands, going as far as to assert any Chinese attack on the islands would invoke Article 5 of the US-Japan Security Treaty.