Taiwan's defense ministry says nine Chinese military aircraft crossed the median line of the Taiwan Strait at around noon on Friday.

The ministry said the planes crossed the northern, central, and southern median line in five batches for combat patrol. The types of aircraft or flight routes were not disclosed.

The ministry condemned the crossings as an "irrational act." It also said, "Armed forces have monitored and responded to the situation with our assets without escalation." The monitoring was conducted by military aircraft, vessels and land-based missile systems.

China's action may be intended to show its displeasure over Taiwan President Tsai Ing-wen's stopover in the United States on her way to Central America.