Taiwan separatists and their activities are the "gravest immediate threat" to peace and stability in the Taiwan Straits and the "biggest barrier" to the peaceful reunification of the country, according to a defense white paper published on Wednesday.

Titled China's National Defense in the New Era and published by the Information Office of the State Council, China's Cabinet, it said the international strategic landscape has undergone profound changes in recent years, and the fight against separatism is becoming more acute, adding that China is the only major country in the world that has yet to be fully unified.

The Taiwan authorities, led by the Democratic Progressive Party, have "stubbornly"pursued independence and refused to recognize the 1992 Consensus that embodies the one-China principle.

"They have gone further down the path of separatism by stepping up efforts to sever the connection with the mainland in favor of gradual independence," it said, adding they also have intensified hostility and confrontation, as well as relying on foreign power to serve their own goal.

To solve the Taiwan question and achieve complete reunification of the country is in the fundamental interests of the Chinese nation and an essential prerequisite to achieving national rejuvenation, the white paper said.

China adheres to the principles of "peaceful reunification" and "one country, two systems", promotes the peaceful development of cross-Straits relations and facilitates the process of peaceful reunification of the country.

"China must be and will be reunited," it said. China has the firm resolve and the ability to safeguard national sovereignty and territorial integrity, and will never allow the secession of any part of the nation's territory by anyone through any means.

"We make no promise to renounce the use of force, and reserve the option of taking all necessary measures," it said. "This is by no means targeted at our compatriots in Taiwan, but at external interference forces and the very small number of Taiwan separatists and their activities."

The People's Liberation Army will resolutely defeat anyone attempting to separate Taiwan from China and safeguard national unity at all costs, it added.