Beijing's defence ministry on Friday denied allegations that a Chinese warship's radar system had locked onto a Japanese destroyer, accusing Tokyo of hyping the "China threat".
The incident, which Japan said happened last week, marked the first time the two nations' navies have locked horns in a territorial dispute that has some commentators warning about possible armed conflict.
The neighbours -- also the world's second and third-largest economies -- have seen ties sour over uninhabited Japanese-controlled islands in the East China Sea known as Senkaku in Tokyo and Diaoyu by Beijing, which claims them.
Tokyo also charges that in the middle of last month a Chinese frigate's radar locked on to a helicopter, in a procedure known as "painting" that is a precursor to firing weaponry.
On both January 19 and January 30, China's defence ministry said in a statement faxed to AFP, the Chinese ship-board radar maintained normal operations and "fire-control radar was not used".
"The Japanese side's remarks were against the facts," it said.
"Japan unilaterally made public untrue information to the media and senior Japanese government officials made irresponsible remarks that hyped up the so-called 'China threat'," it added.
Tokyo had "recklessly created tension and misled international public opinion", it said.
Japan hit back Friday, with Foreign Minister Fumio Kishida saying he "cannot accept" the explanation.
"We were waiting to see how China would perform its duty to give a clear explanation, but the Chinese defence ministry told the Japanese embassy in Beijing Thursday evening that what Japan has announced does not match the facts," Kishida said.
"We have made a cautious and elaborate analysis of this incident at the defence ministry and we have confirmed it," he said.
"We told the Chinese side we cannot accept their argument and asked them for a sincere response," he said.
Defence Minister Itsunori Onodera said Friday the public announcements had been made "after a special unit analysed data on the radar contact and confirmed it. There is no mistake about it."
Prime Minister Shinzo Abe said he wanted to change Japanese diplomacy to something "that is still polite and quiet, but vocal about our position once our sovereignty or national interest is being challenged."
The long-running row over the islands intensified in September when Tokyo nationalised part of the chain, triggering fury in Beijing and huge anti-Japan demonstrations across China.
Beijing has repeatedly sent ships and aircraft near the islands and both sides have scrambled fighter jets, though there have been no clashes.
Abe on Thursday called the radar incident "extremely regrettable," "dangerous" and "provocative" but also said that dialogue must remain an option.
"We will not close the window of dialogue. This is most important," said Abe. "I would like China to return to a more open attitude towards our strategic partnership."
The seabed near the island chain, which is also claimed by Taiwan, is believed to contain mineral reserves.