Taiwan, in a warning to China, has asserted its right to attack People's Liberation Army Air Force warplanes that violate its airspace beyond the midline in the Taiwan Strait.

The Ministry of National Defense issued the self-defense warning late Monday after two China antisubmarine aircraft earlier in the day intruded into Taiwan's air defense identification zone, or ADIZ, in the southwest but didn't cross the midline.

It was the latest in a series of aerial incursions by China. Planes of its air force Friday and Saturday entered the ADIZ and were warned to turn back. The intrusions saw Taiwan scramble interceptors.

On Monday, Taiwan said its armed forces had the right to self-defense and to counter attack in the face of China's "harassment and threats." Its defense ministry said it had "clearly defined" procedures for a first response as a result of a "high frequency of harassment and threats from the enemy's warships and aircraft this year."

It said Taiwan would, however, abide by its guideline of "no escalation of conflict and no triggering of incidents." It won't provoke China but isn't "not afraid of the enemy."

The recent incursions by China were triggered by the visit to Taiwan Sept. 17 by Keith Krach, U.S. Under Secretary of State for Economic Growth, Energy and the Environment. Krach attended a memorial service for former Taiwan President Lee Teng-hui on Saturday. Lee, who died July 30, was Taiwan's fourth president.

He was also the first Taiwan president to champion the idea of Taiwan being a separate and distinct entity from mainland China.

"That makes him the No. 1 or No. 2 most-hated person on Beijing's list for Taiwan," said Yinan He, an associate professor at the Department of International Relations at Lehigh University. "So by paying tribute to this person the Trump administration is really poking Beijing in the eye."

On Sept. 10 Taiwan's defense ministry rebuked China for sending warplanes into the ADIZ on several occasions during drills by the People's Liberation Army Navy within 166 kilometers of Taiwan.

"These military actions have seriously roiled Taiwan and threaten peace and stability in the region," said vice defense Minister Chang Che-ping at a news conference. Some 30 China air force planes took part in the drills and entered Taiwan's ADIZ at least 21 times.

Krach was the second high-level Trump administration to visit Taiwan in two months. Health and Human Services secretary Alex Azar visited in August.