China sent fighter jets across the waterway to the south of Taiwan on Monday, days after President Xi Jinping warned the self-governing island nation against trying to secede from China. In response, Taiwan sent its aircraft to shadow the fighter jets, Reuters reported, quoting the country’s defence ministry.

China had sent an unspecified number of Xian H-6 bombers, Su-30 fighter jets and Y-8 transport aircraft over the Bashi Channel between the Philippines and southern Taiwan, the Taiwanese government said. Taiwan’s aircraft then followed them until they returned to their base.

Taiwan governs itself democratically, but China considers the island nation an integral part of its territory, and relations remain strained. Beijing has been more hostile since Tsai Ing-wen was elected Taiwan’s president in 2016, because she refuses to recognise the “one China” policy.

On March 20, Xi Jinping, newly elected for a second term as president, warned that Taiwan would be “punished by history” if it tried to separate from China. He said his country would push for the “peaceful reunification of the motherland” so that more Taiwanese people get the opportunities of China’s development.

The next day, Taiwan sent ships and aircraft to shadow a group of Chinese aircraft carriers across the Taiwan Strait.