TAIPEI, Taiwan (AP) — Taiwan’s Defense Ministry accused China on Saturday of harassment and trying to affect public morale by repeatedly sending balloons over the self-governing island.

A ministry analysis found that the paths of the balloons posed a serious threat to international passenger flights, according to a report by Taiwan’s official Military News Agency. The ministry called for an immediate end to the activity to ensure flight safety,

“The ministry urged the people (of Taiwan) to clearly understand the Chinese Communist Party’s cognitive combat methods and face it rationally and calmly so as to avoid being affected by it,” the report said.

The purpose of the balloons is unclear, and a Chinese state media outlet has accused Taiwan’s ruling Democratic Progressive Party and Taiwanese and American media of hyping what it says are harmless weather balloons. The balloon incidents come ahead of a Jan. 13 presidential election in Taiwan in which the island’s relations with China are a major issue.

Taiwan’s Defense Ministry has reported several instances of Chinese balloons flying near or over the island in the past month. It said Saturday that two balloons had been detected over the Taiwan Strait on Friday, one 33 nautical miles and the other 51 nautical miles off the island’s northwest coast.

China views Taiwan, which is about 160 kilometers (100 miles) off China’s east coast, as a renegade province that must come under its control. Chinese leader Xi Jinping said in an annual New Year’s address this week that Taiwan would “surely be reunified” with China in the future.