BEIJING, Jan. 30 (Xinhua) -- A leading official from the International Air Transport Association (IATA) has spoken in support of the Chinese mainland operating an air route to ease traffic congestion.

The M503 route, which has been used since March 2015, is not a new route. Its position and design have been approved by the International Civil Aviation Organization, the official said in a response to concerns from the Taiwan civil aviation authority.

The response, dated Jan. 19, was relayed to Xinhua recently by an authoritative source who declined to be named.

The M503 route was launched to ease flight congestion on the A470 route and has made flying safer as the sky over the Yangtze River Delta and the Pearl River Delta continues to get busier, the IATA official said.

The aviation industry considers operating the M503 route a "positive" move to ease congestion in Shanghai airspace, the official said.

Airlines from Hong Kong, Macao and southeast Asian regions began flying north to south on the M503 route in March 2015.

The Taiwan aviation authority, however, expressed concerns over the start of the south-to-north operation on the route on Jan. 4 this year.

The Chinese mainland insists that there is no ground for concerns.

The Taiwan Affairs Office of the State Council said the south-to-north operation of the M503 route is close to the mainland in the Taiwan Strait and in the Shanghai Flight Information Region.

"It involves no Taiwan flight route or destination and will not affect Taiwan flight safety," said Ma Xiaoguang, a spokesperson for the Taiwan Affairs Office of the State Council, at a recent press conference.