Taiwan’s defense ministry has accused China of continuing a “harassment campaign” against the island nation by sending high-altitude balloons over Taiwan in what it describes as part of “cognitive warfare,” Business Insider reported.

China launched six more balloons over the island late last week, which crossed Taiwan’s airspace at different times on Sunday, Taiwan’s ministry said.

Taiwan’s military says 5 balloons crossed the northern part of the island at an altitude of 6,000 meters and above, while a sixth flew over the southern city of Pingdong at an altitude of only 4,500 meters. Military forces in Taipei also spotted aircraft and four Chinese Liberation Army ships approaching the island.

Since the beginning of the year, Taiwan has said it has spotted dozens of balloons launched from China flying over its territory ahead of the January 13 presidential election.

Taiwan’s Ministry of Defense said they were part of a “cognitive war” and called on the public to assess the situation “rationally and calmly” on January 6, France24 reported.

Chinese diplomacy claims that it is “not aware” of the situation reported by Taiwan

When asked about it, a spokesman for China’s foreign ministry told Axios on Wednesday that he was unaware of the situation and that it was “not related to China’s foreign policy issues.”

China’s high-altitude balloons also caused tensions with the United States last year, when Washington’s military shot down one such balloon that flew over US territory in February.

The US says the balloons are being used by China for espionage purposes, while Beijing says they are weather balloons or other types of scientific measurements.

Tensions between China and Taiwan, already at their highest level in a decade, escalated after the island nation elected Lai Chin-te, a candidate Beijing described as a “grave danger,” as president.