TAIPEI--China’s air force approached Taiwan on Friday for the fourth time in four days, Taiwan’s military said, as China steps up maneuvers near the island that Beijing claims as its own territory.

Taiwan’s air force said the J-10 fighter jet was involved in the approach but did not say whether only one aircraft or more had entered Taiwan’s air defense identification zone to the island’s southwest around midday (0400 GMT).

The Chinese air force was given a verbal warning to leave, and Taiwanese jets “responded,” Taiwan’s air force said, without giving further details.

The aircraft then withdrew and the situation returned to normal, it said in a brief statement.

In the past week-and-a-half, the Chinese air force has buzzed Taiwan six times, according to Taiwan’s military.

China has not said in public why it has increased its activity near the island but has previously described such drills as routine and intended to show China’s determination to defend its sovereignty.

Taiwan’s air force, which is well trained and is modernizing its U.S.-made F-16 fighter jets, routinely patrols above the sensitive Taiwan Strait that separates the island from its much larger neighbor.

China has never renounced the use of force to bring democratic Taiwan under its control, though the island has shown no interest in being ruled by autocratic Beijing.

Taiwan has complained China has stepped up its military activity, including sending aircraft carriers near the island, since the outbreak of the COVID-19 pandemic.