Taiwan says it scrambled its air force to drive away Chinese military planes that had flown into its airspace late Monday.

The island’s Defense Ministry said a group of Chinese fighter jets and surveillance planes flew into the waters off of Taiwan’s southwestern coast as part of nighttime exercises, coming close to its air defense identification zone.

Beijing has been conducting numerous naval and aviation exercises in the Taiwan Strait since the election of Taiwan President Tsai Ing-wen in 2016 as a means of pressuring Taipei from declaring its independence.

China and Taiwan split after Chaing Kai-shek’s Nationalist forces settled on Taiwan after they were driven off the mainland by Mao Zedong’s Communists after the end of the 1949 civil war.

China considers the self-ruled island a breakaway province and has vowed to annex the island by any means necessary, including a military invasion.