SUCH reports have been heard before and smack of wishful thinking. But there are more reasons than usual to believe China's promises that it is trying to rein in its unruly, pugnacious little ally, North Korea. South Korea's president, Lee Myung-bak, has said that China has promised not to side with North Korea if it stages further provocations towards the South. That would be a big shift. Last year China failed to condemn either the sinking by North Korea of a South Korean naval vessel in March, or the shelling in November of a South Korean island. Now Chinese scholars and officials do indeed seem to be sending strong signals to North Korea that enough is enough.

In June Liang Guanglie, China's defence minister, told a regional-security forum in Singapore that China had done much more in communicating with North Korea “than you can imagine”. At another conference, in Kuala Lumpur, Zhu Feng, a professor at Peking University, contradicted a North Korean participant who argued that the security issue on the Korean peninsula was one of reunification and a legacy of the cold war. It was also a result, Mr Zhu said, of the unchanged nature of the North Korean regime and its behaviour. North Korea, he argued, “risks biting the Chinese hand that feeds it.”

China has been exasperated with North Korea before, not least in 2006, after its first test of a nuclear weapon. Mutual suspicion and animosity go back much further. In a recent paper*, You Ji, who teaches at the University of New South Wales, reports that Kim Jong Il, North Korea's dictator, never forgave China for its disapproval of the hereditary succession in which he took over from his father, Kim Il Sung. Sulking, he did not visit China once from 1983 to 2000.

Since May last year, however, he has been three times. That is a symptom of his regime's greater dependence on China, which accounts for four-fifths of its trade and energy needs, and most of the food aid it gets to avert renewed famine.

The corollary of greater North Korean dependence should be greater Chinese influence. But in the past the North Korean regime has always managed to fend off unwelcome pressure by silently playing on two big Chinese strategic fears. One is that a spurned North Korea might provoke South Korea and America, triggering a cycle of retaliation and even war. The second is that it might collapse in chaos with a mass exodus of refugees into China. Any collapse would presumably be followed by reunification of the Korean peninsula under the prosperous, American-allied South. That could mean American troops stationed in a country bordering China, complicating its strategy should, for example, it ever find itself in a confrontation with America over Taiwan. Until now, the North's primitive nuclear weapons have not seemed to worry China too much. After all, they do not threaten it, and if they help the regime survive, they serve a Chinese purpose.

Last year's events may have changed these calculations. In South Korea President Lee faced criticism for not responding more robustly to the attacks. Some have called for American battlefield nuclear weapons to be stationed there, alarming China. There is also the risk that any new provocation, or mishap, could quickly get out of hand. In mid-June two South Korean marines shot their rifles at a civilian airliner landing at Incheon, the airport for Seoul, mistaking it for a North Korean plane. You Ji thinks that the Korean peninsula may have supplanted Taiwan as the potential war most worrying China. China's North Korea-watchers also fret that the next dynastic succession, from Kim Jong Il to the plump but callow Kim Jong Un, may be more than the system can stand, leading to a military junta or civil war.

One form of Chinese pressure on North Korea is a renewed drive to help it reform the moribund economy. After Mr Kim's most recent trip to China the North announced that China would help develop three special economic zones. In the past, similar schemes have come to nought, perhaps because the Kim regime fears economic liberalisation would make the example of South Korea look even more appealing, and lead to an implosion.

Another sort of Chinese pressure is to coax North Korea back to the six-party process that it hosts for the two Koreas, America, Japan and Russia to discuss North Korean “denuclearisation”. China has proposed preliminary steps—starting with inter-Korean talks, followed by North Korean-American dialogue.

The first step has so far proved out of reach because of South Korea's demand for some sort of apology for last year's outrages. That might be finessed by holding lower-level talks initially. But the big obstacles remain, and China seems unable to overcome them. America does not want to reward North Korean bad behaviour; and nobody believes it will ever fully abandon its nuclear capability. Yet at a recent nuclear conference in Seoul organised by the Asan Institute, a think-tank, Gary Samore, of America's National Security Council, made clear that the United States can never accept a nuclear-armed North Korea.

Superpowerless

In fact, America will have to resume dialogue one day. There is no other way to work towards at least capping North Korea's nuclear weaponry, which, unmolested and uninspected, it is presumably doing its best to enhance. But talks might be further delayed if the North flexes its muscles with a third nuclear test—perhaps even with a bomb made not from its dwindling stock of plutonium but from highly enriched uranium, for which last year it admitted it had a programme, shocking the world. Judging from its recent signals, China should be exerting what influence it can to prevent a new test. What is really frightening about the Kim family, however, is that not even mighty China can tell it what to do.

* “Dealing with the ‘North Korea Dilemma': China's Strategic Choices” by You Ji. S. Rajaratnam School of International Studies Working Paper 229, June 2011