The M503 flight path is for civil aviation in the Shanghai Flight Information Region, and operating the route is aimed at easing traffic congestion and ensuring flight safety, a Chinese mainland official said on Wednesday, in response to the secessionist Democratic Progressive Party (DPP)'s hype of and opposition to the mainland's adjustment to Taiwan Straits flight routes.

The Civil Aviation Administration of China on Tuesday announced that from February 1, the deviation of the M503 flight route from north to south will be canceled, a change which the Taiwan authorities interpreted would see southbound aircraft flight paths above the Taiwan Straits come closer to Taiwan's self-claimed "median line," "flight information region," and "air defense identification zone."

M503's connecting routes W122 and W123 from west to east will be also activated. Those routes link M503 respectively with the mainland cities Fuzhou and Xiamen in East China's Fujian Province.

Approved by the International Civil Aviation Organization (ICAO), the mainland established the M503 flight path and its connecting routes W121, W122 and W123 in January 2015 to ease traffic pressure on the A470 flight path. After negotiations with Taiwan authorities, the mainland side agreed to a deviation in the M503 flight path of six nautical miles (11kilometers) to the west in the direction of the mainland, since the island believed that the M503 route was only 4.2 nautical miles from the "median line" of the Taiwan Straits. The mainland decided at that time not to activate the connecting W121, W122 and W123.

Taiwan's mainland affairs office on Tuesday expressed opposition, saying the move "disregards aviation safety and shows disrespect for Taiwan," as it appears to be a deliberate attempt to use civil aviation as a cover for political, and possibly military intentions aimed at altering the status quo in the Taiwan Straits."

In response, Chen Binhua, a Taiwan Affairs Office spokesperson, said on Wednesday that the M503 route is a civilian route within the Shanghai Flight Information Region, and was launched to ease congestion in the relevant airspace and to safeguard aviation safety.

He stressed that Taiwan is an inalienable part of China's territory, and there is no such thing as the "median line" of the Taiwan Straits.