BEIJING, Dec. 28 (Xinhua) -- A mainland spokesman Wednesday said the Taiwan issue is a domestic affair, and the United States should carefully handle it by abiding with 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 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 a 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 U.S. arms sales to Taiwan.

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

"We always handle Taiwan-related issues based on the one-China principle, and any attempt to create 'two Chinas' or 'one China, one Taiwan' is doomed to failure. The historical trend is irresistible," An said.

Since May 20 this year, the Democratic Progressive Party refused to accept the 1992 Consensus that upholds both sides of the Taiwan Strait belong to one China, which has affected the peaceful development of cross-Strait relations.

"The impact can be felt in many fields," An said. "We uphold the one-China principle and oppose 'Taiwan independence,' and our stance is supported by the international community."