The US is planning on "cooperation" between its National Guard and Taiwan's military, Taiwan President Tsai Ing-wen said on Tuesday, deepening security ties in the face of what Taipei's government complains is a rising threat from China.

The US is Chinese-claimed Taiwan's most important international supporter and arms supplier, despite the lack of formal diplomatic ties. China has been stepping up its military activities near Taiwan to assert its sovereignty claims.

China's military said last week...