A mainland spokesman Wednesday said the Taiwan issue is a domestic affair of China and the United States should carefully handle it by abiding by the one-China policy.

An Fengshan, spokesman for the State Council's Taiwan Affairs Office, said that the Taiwan issue is a matter concerning national sovereignty and territorial integrity of China.

It is also the "most sensitive and complicated issue in China-U.S. relations," he said at a press conference.

He was asked to comment on the United States' 2017 National Defense Authorization Act, which includes the provision on military cooperation with Taiwan.

"We hope the United States will abide by the one-China policy and the three China-U.S. joint communiques, and carefully handle issues related to Taiwan," the spokesman said.

China firmly opposes official and military relations between the United States and Taiwan in any form, he said.

An reaffirmed China's clear and consistent opposition to arms sales by the United States to Taiwan.

In response to another question, An said that a Chinese navy formation, including the aircraft carrierLiaoning, headed toward the West Pacific on Dec. 24 for scheduled blue water training, which was carried out in accordance with the annual plan made by the navy.