China has denounced a comment by Japan's Foreign Minister Taro Aso after he called Taiwan "a country".
Mr Aso has upset China before
Japan's foreign ministry denied Mr Aso's remark was a change of Tokyo's official position, which recognises China's claim to Taiwan.
China also rejected a Japanese proposal to jointly develop disputed gas fields in the East China Sea.
Ties between China and Japan have deteriorated recently because of rows over energy and history.
Mr Aso made the comment about Taiwan when talking to a parliamentary committee.
"(Taiwan's) democracy is considerably matured and liberal economics is deeply ingrained, so it is a law-abiding country," he said. "In various ways it is a country that shares a sense of values with Japan."
But Tokyo's foreign ministry later denied this was meant to imply that it was changing its official stance on Taiwan, which it does not diplomatically recognise, in favour of China.
"There is no change in Japan's position on the Japan-China agreement of 1972 that stated there is one China," said Keiji Kamei, of the China division in the Foreign Ministry
Beijing has nevertheless complained.
"China strongly protests this crude interference in its internal affairs," said Foreign Ministry spokesman Qin Gang, expressing "surprise that a high-ranking Japanese diplomat would make such remarks".
China and Taiwan have been governed separately since a civil war ended in 1949, but China still sees Taiwan as its territory and has threatened to use force if the island moves towards declaring independence.
Gas talks stalled
Japan's outspoken foreign minister has riled Beijing on several occasions in recent weeks, including accusing China of using female spies to seduce and blackmail Japanese diplomats, and suggesting Taiwan's high educational standards were thanks to Japan's colonial rule.
The two neighbours have been arguing about a range of issues in recent months, including resources in the East China Sea and Tokyo's approach to its wartime past.
China and Japan's exclusive economic zones (EEZs) overlap
Japan claims EEZ extends 200 nautical miles from its shore, while China claims EEZ extends to edge of its continental shelf
Two countries have never agreed a maritime border
The UN says it will arbitrate by May 2009
Also dispute ownership of Senkaku/Diaoyu islands
Talks on disputed gas fields failed to make progress this week, with Japan rejecting a Chinese proposal that for the joint exploitation of deposits around a group of islands hotly contested by both countries.
Then Beijing on Thursday rejected Tokyo's suggestion - in the an area of the East China Sea that straddles both sides of what Tokyo says is the maritime boundary.
"The meridian line was unilaterally proposed by Japan," Mr Qin told reporters. "China never accepted that and will never accept that."
The two sides also revisited their ongoing row over a controversial war shrine this week.
Chinese Foreign Minister Li Zhaoxing said on Tuesday the visits to Yasukuni Shrine, which honours 2.5m war dead including 14 World War II criminals, had been described as "stupid" and "not moral".
Japanese Chief Cabinet Secretary Shinzo Abe said such remarks were inappropriate and offensive.