Japan’s Self-Defense Force held its first serious drill to defend the disputed Senkaku islands today.

China also claims the tiny islands in the East China Sea, calling them the Diaoyu.

The dispute has soured ties, especially since 2012 when Japan’s government purchased three of the islands from their owner.

The drill took place on a deserted island in nearby Kagoshima prefecture.

China and Russia’s militaries are now training in the same seas.

In the drill, Japan’s island defense troops practiced retaking the islets.

Japan’s government is now considering how to respond to a possible “gray zone” event in which armed groups dressed as fishermen land on the islands.

The US is obligated to defend the Senkakus under the Japan-US defense treaty.

US President Barack Obama made this explicit for the first time when he visited Tokyo last month.