China on Tuesday brushed aside calls from Japan to hold a leaders' summit as "grandstanding", while Japan's finance minister said Tokyo should make clear it would use its navy to defend islands at the core of a dispute with Beijing.

Ties between the world's second- and third-largest economies have been strained for months because of a row over the islands, known as the Senkaku in Japan and the Diaoyu in China, as well as disputes over the countries' bitter wartime past. Japanese Prime Minister Shinzo Abe is keen to improve ties and has called for dialogue with China, though he has rejected any conditions on talks. China has shown no inclination to respond to the overtures. "A meeting between leaders is not simply for the sake of shaking hands and taking pictures, but to resolve problems," Chinese deputy foreign minister Li Baodong told reporters ahead of a G20 summit next week that both Chinese President Xi Jinping and Abe will attend.

"If Japan wants to arrange a meeting to resolve problems, they should stop with the empty talk and doing stuff for show," Li said, when asked about the possibility of a meeting of Chinese and Japanese leaders on the sidelines of the G20. Aircraft and ships from both countries have played cat-and-mouse games near the islands for months, ratcheting up tension. Japan's coastguard said on Tuesday three Chinese coastguard vessels had briefly entered what Japan considers its territorial waters near the disputed islands. China said the trip was a routine patrol in its own waters.

Japan's finance minister, Taro Aso, who doubles as Abe's deputy, said the government must make clear its intent to defend the islands or risk what happened when Argentine troops landed on the Falkland islands in 1982, triggering war with Britain.

"When Britain deployed aircraft carriers to the Falkland Islands, it did not convey its intentions to protect the islands. Argentine saw that (Britain) had no intention of protecting the Falklands and so invaded," Aso said in a lecture to parliamentarians in Yokohama, near Tokyo.

"Fighting ability, national consensus and informing other countries (of our intention to use force) can act as a deterrent only if these three are all present," Aso said.

"We must clearly convey our intention to protect the Senkaku with the Maritime Self-Defence Forces. In that sense, we cannot avoid increasing Defence spending ... This is the reality we're in while facing the situation in the East China Sea."

The legacy of Japanese militarism in the 1930s and 1940s also haunts Sino-Japanese ties.

China's Li said denials by some Japanese politicians of the country's wartime past do not help. "Under these conditions, how can we organise the kind of leaders' summit that Japan wants?" Li said.

China reacted angrily this month when Abe sent an offering to a shrine for war dead, which also honours war criminals, while cabinet members visited it in person.

China suffered under Japanese rule, with parts of the country occupied from the 1930s. Japanese leaders have apologised in the past but many in China doubt their sincerity, partly because of contradictory remarks by politicians.

"What Japan has to do now is show vision and courage, properly face up to history and take a proper attitude and real actions to get rid of the obstacles which exist for the healthy development of bilateral ties," Li said.

Meanwhile, three Chinese coastguard ships on Tuesday entered disputed waters near East China Sea islands at the centre of a bitter row with Tokyo, Japanese officials said.

The vessels sailed into the 12-nautical-mile band around the Tokyo-controlled Senkaku islands - which Beijing calls the Diaoyus - at around 0030 GMT, the Japanese coastguard said.

The incursion came a day after Japan's defence minister said Tokyo could be a key participant if conflict breaks out in Asia as he warned China was seeking to exploit difficulties between allies.

It was the latest in a series of forays by Chinese ships in a year-long spat between Tokyo and Beijing that has sent relations plummeting.

The islands - believed to harbour vast natural resources below their seabed - are seen as a potential flashpoint that some observers fear could lead to armed conflict between the Asian giants.