A Chinese mainland spokesman denounced the ruling Democratic Progressive Party in Taiwan for cooperating with foreign forces to hype up the assertion that the Taiwan Straits separating the island from the mainland is an "international waterway".

Ma Xiaoguang, spokesman for the Taiwan Affairs Office of the State Council, said at a news conference on Wednesday that the move by the DPP authority was part of separatist efforts to achieve "Taiwan independence".

"It has harmed the interests of compatriots on both sides of the Straits and betrayed the interests of the Chinese nation," he said. "Such behavior is beneath contempt."

Ma's remarks came after the DPP administration's denial of the mainland's claim to exercise sovereignty over the passage between the two sides that ranges in width from about 70 nautical miles at its narrowest and 220 nautical miles at its widest.

"Taiwan is an inalienable part of China's territory," Foreign Ministry spokesman Wang Wenbin said at a news conference on Monday, adding that international maritime laws don't define international waters.

According to the United Nations Convention on the Law of the Sea and Chinese laws, the waters of the Straits, extending from both shores toward the middle of the Straits, are divided into several zones, including internal waters, territorial sea, contiguous zones and the Exclusive Economic Zone.

"China has sovereignty, sovereign rights and jurisdiction over the Straits. At the same time, it respects the lawful rights of other countries in relevant waters," Wang said.

"It is a false claim when certain countries call the Straits 'international waters' in order to find a pretext for manipulating issues related to Taiwan and threatening China's sovereignty and security," he said.

On Tuesday, Taiwan's "foreign affairs" spokeswoman Joanne Ou said such comments were a "fallacy" and that the island supports the freedom of navigation operations conducted by the United States.

On Wednesday, Taiwan's executive head Su Tseng-chang said the Straits was by "no means China's inland sea" and is a maritime area for free "international navigation".