ARMED conflict between Japan and China over the five tiny, uninhabited Senkaku or Diaoyu islands still seems improbable. But that does not make it impossible. This week it was revealed just how close their stand-off has come to a shoot-out. On February 5th the Japanese government claimed that six days earlier a Chinese warship had beamed “fire-control” radar at a destroyer belonging to Japan’s Maritime Self-Defence Force some 3 kilometres (2 miles) away—a step towards shooting a missile at it. “It was a unilateral, provocative act and extremely regrettable,” Shinzo Abe, Japan’s prime minister, told the Diet, or parliament, on February 6th.

The incident, which occurred about 100km from the Senkakus, fits a pattern of Chinese sabre-rattling. On January 19th a Chinese frigate is also thought to have “locked on” to a Japanese ship-based helicopter. Since September, when Japan’s government “nationalised” three of the islands by buying them from their private owner, China has been challenging not just Japan’s claim to sovereignty over the Senkakus, but also its control of them. Ships and aircraft from both countries have patrolled the islands, and each has scrambled jet fighters in response to “incursions” by the other, leading to a string of aerial and maritime near-misses.

The American government, which takes no official position on who owns the islands, has confirmed that they are covered by its security treaty with Japan. Its diplomats have scurried to Asia in recent weeks, urging restraint and “cooler heads”. During the cold war America and the Soviet Union at least established mechanisms to prevent a serious conflict being caused by miscalculation or accident. China and Japan have very few such mechanisms.

Oddly, the January 30th incident came just as tensions seemed to be easing. There was talk of a fence-mending summit between Mr Abe, who took office in December, and Xi Jinping, China’s new leader. China has been using mainly civilian agencies rather than the navy to patrol the islands. And the Chinese press has not been uniformly bellicose. In Global Times, a Communist Party newspaper whose default mode is tub-thumping nationalism, two commentators this week separately urged caution, recalling China’s history of being set back in its development by Japanese aggression—in the 1890s and again in the 1930s and 1940s.

As a result, some Japanese politicians believe the provocation must have been a low-level decision by a commander on the ship. Katsuyuki Kawai, a foreign-affairs spokesman for the ruling Liberal Democratic Party, thinks the incident would have embarrassed China, since “it gives the impression that China is a rogue state”. He says that the idea that China’s forces are out of control is the Japanese government’s “biggest fear”.

The alternative, however—that this is a deliberate policy sanctioned at the highest level—may be even scarier. And a new study of China’s foreign policy by Linda Jakobson of the Lowy Institute, an Australian think-tank, argues that Chinese treatment of the islands is in fact tightly co-ordinated, with Mr Xi in direct charge as the head of a new office set up to deal with the crisis. She cites an anonymous official involved in the decision-making, who suggests that Mr Xi knows the dangers but is being given “exaggerated assessments” by underlings keen that he should take a tough stance.

Akihisa Nagashima, a security adviser in Japan’s previous government, thinks China is testing the strength of Japan’s alliance with America. Others argue that China’s objective may also be to undermine Mr Abe, who vowed in his general election campaign to take a strong stand against Chinese claims to the islands.

A Xi-Abe summit is not guaranteed to take place. As new leaders keen to look strong, neither will find it easy publicly to offer concessions. Ms Jakobson suggests that, to defuse tensions, the two countries should agree to share fishing rights and to patrol on alternate days. But that is to assume that effective joint control is neither too much for Japan to accept, nor too little for China.

It would require Mr Abe to concede, at least implicitly, that the islands’ sovereignty is disputed, which flies in the face of Japan’s position. Mr Abe is due in Washington, DC, later this month. He must be hoping that President Barack Obama will reaffirm the importance of America’s security treaty with Japan, and that China will be deterred and will moderate its behaviour. Little that has happened since September, however, suggests that China is inclined that way.