BEIJING - Japan's Prime Minister Shinzo Abe has demanded that Beijing apologise and admit that a Chinese frigate directed a radar lock on a Japanese destroyer in international waters, as the two countries engaged in a fresh round of invective over military movements near a disputed group of uninhabited islands.

His demand came after Beijing flatly denied Tokyo's accusation over the weapons-targeting radar lock on Jan 30. Yesterday's exchange, which also saw Tokyo summoning the Chinese Ambassador, fuelled tensions that for months have bedevilled relations between the two Asian powers.

"We wish for China to acknowledge the radar lock, apologise for it and make efforts to prevent it from recurring," Mr Abe told the BS Fuji TV station yesterday.

The comments came after he signalled yesterday that he will implement a more robust foreign policy amid disputes with Russia and China that underscore his push to boost defence spending.

Japan on Thursday said two Russian fighter jets briefly entered its air space near long-disputed northern islands, prompting Tokyo to scramble combat fighters. Russia denied the accusation.

"When our sovereignty and national interests are threatened, we must change our foreign policy to firmly express our point of view," Mr Abe told Parliament.

He denounced China's use of radar on the Japanese vessel, calling it a "one-sided provocation".

International relations professor Kunihiko Miyake from Ritsumeikan University said: "We've been too silent in some ways."

Mr Abe's reaction shows "that by disclosing the information, he wanted to send a strong warning together with the rest of the international community that such provocation cannot be tolerated", Prof Miyake added.

Earlier yesterday, China rejected the Japanese allegation, saying Tokyo's intrusive tracking of Chinese vessels was the "root cause" of the renewed tension.

In a statement issued yesterday, China said the Chinese shipboard 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'."

Tokyo had "recklessly created tension and misled international public opinion", it added.

Chinese Foreign Ministry spokesman Hua Chunying added later: "Japan again deliberately spread false information to smear China's image and play up the 'China threat'. This has created tension and misled international opinion. We cannot help but ask what is Japan's true intention."

Japan hit back, 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 on Thursday evening that what Japan has announced does not match the facts," Mr 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."

Japan's Vice-Foreign Minister Chikao Kawai told Ambassador Cheng Yonghua that China's response was "totally unacceptable" and called for Beijing to "sincerely fulfil its responsibility for an explanation" and take measures to prevent similar incidents.

Japanese Defence Minister Itsunori Onodera said this week that the incident could have become dangerous quickly, and may have been seen as a threat of military force under United Nations rules.

The long-running row over the islands intensified in September last year when Tokyo nationalised part of the chain, triggering fury in Beijing and huge anti-Japan demonstrations across China.

Mr Abe said on Thursday that dialogue must remain an option. "We will not close the window of dialogue. This is most important. I would like China to return to a more open attitude towards our strategic partnership," he said.

REUTERS, BLOOMBERG, AGENCE FRANCE-PRESSE