Taiwan reported China’s Liaoning aircraft carrier group sailing to the island’s south. The sighting came hours after the Chinese military put out a video saying it was “prepared for battle.”

Taiwan’s Defense Ministry said Sunday it was “on alert” after a Chinese aircraft carrier was detected to the south of the island.

The incident comes three days after Taiwan’s president angered Beijing during a speech to mark the self-ruled island’s National Day.

China considers Taiwan as part of its territory and tensions between the two have spiked in recent years over the near-constant deployment of Chinese ships to waters near the island.