HONG KONG — China has opened a third extension of the controversial M503 flight route near Taiwan, just days before Taipei’s annual Han Kuang military exercises.

Beijing’s civil aviation authority announced the W121 extension “to improve airspace efficiency and passenger safety.” But Taiwan has long opposed the M503 route, which lies just west of the Taiwan Strait’s median line, accusing China of using civil aviation for political and military aims to undermine the status quo.

The median line — once an unofficial buffer — has been increasingly crossed by Chinese warplanes as Beijing presses its sovereignty claims over the island.

The new W121 extension, running west to east toward Taiwan, follows last year’s openings of W122 and W123. China’s Taiwan Affairs Office called the move “beneficial” to both sides.

Taiwan’s Mainland Affairs Council has yet to respond. The Han Kuang drills, simulating a Chinese blockade and invasion, begin July 9 and will last 10 days.