When North Korea tested a nuclear device last year, China issued bland criticism and urged Pyongyang to resume diplomacy. After a South Korean navy ship was sunk, most likely by a North Korean torpedo, Beijing sent its sympathies but called the evidence inconclusive.

Now that North Korea has unleashed an artillery barrage on a South Korean island that killed four people — including two civilians — and raised tensions in the heavily armed region, Beijing again appears unwilling to rein in its neighbor.

For all China's growing international might, its tolerance of North Korea's wayward behavior shows how differently Beijing sees the world — or at least its corner of it.

"There is zero chance of China, either in open or in private, putting major substantive pressure on North Korea," said Shi Yinhong, professor of international relations at Beijing's Renmin University.

As impoverished North Korea's most important diplomatic ally and source of crucial food and fuel assistance, China holds the sort of influence that could bring Pyongyang to heel. But keeping the region stable so that China may continue its upward trajectory is the Chinese leadership's No. 1 priority. If that means putting up with the occasional North Korean provocation, experts say, so be it.

China has reasons to worry if the current, tenuous peace dissolves. It lost an estimated 400,000 troops in the 1950-53 Korean War. Another conflict or a meltdown of North Korea's dictatorship could send hundreds of thousands of North Koreans across the border, burdening Chinese provinces that only in recent years recovered from painful restructuring of the planned economy. Worse, a South Korean victory would bring to China's threshold a U.S. ally that hosts American military forces.

Following Tuesday's bombardment, Beijing has so far shied away from calling North Korea to task.

Maximum restraint

In the highest level comments since the incident, Chinese Premier Wen Jiabao said China "opposed military provocations in any forms" and called for a resumption of talks on North Korea's nuclear disarmament that stalled two years ago.

"All concerned parties should exert maximum restraint, and the international community should make more efforts conducive to easing up the tensions," Wen said in remarks made while traveling in Russia and carried on the Foreign Ministry's web site.

Wen never mentioned North Korea by name.

State media, the only media there is in China, maintained a mostly studied neutrality, describing the skirmish as an exchange of fire.

China's strategy to steady North Korea has exacted costs. Beijing's refusal to criticize North Korea after the sinking of South Korea's naval corvette, the Cheonan, in which 46 sailors died, offended Seoul, a key investor and trade partner which had been drawing closer diplomatically. In the United Nations, China shielded North Korea from punishment over the incident.

China's protection of North Korea at times seems so unreasonable that it adds to misgivings among Japan, Vietnam and other nations already upset over Beijing's more forceful assertion of its territorial claims in the East and South China seas.

Relations with Washington may suffer too, just two months before Chinese President Hu Jintao wants to pay a pomp-filled state visit.

President Barack Obama has called upon Beijing to restrain its ally. State Department spokesman P.J. Crowley said U.S. diplomats had delivered a message to China that it was "pivotal" to changing North Korea's behavior, adding that Beijing has a responsibility to make it clear to Pyongyang that deliberate attempts to inflame tensions with Seoul are not acceptable.

Beijing's support

But some American officials and independent analysts have questioned the amount of influence that China actually has with its neighbor, and warned against relying on the Chinese to change North Korean actions.

Far from backing away from Pyongyang, China has in recent years doubled down on its support. As Japan, South Korea and others have reduced trade and aid in recent years in response to North Korean nuclear and missile tests, China has stepped up deliveries of food and other assistance.

China accounted for half of all North Korea's imports and took a quarter of its exports in 2008, according to the U.S. Congressional Research Service. That was before the North's relations with South Korea began souring, taking tourism and investment programs with them.

Politically, Beijing has upped its engagement too, sending a stream of leaders to Pyongyang and twice hosting reclusive North Korean leader Kim Jong Il this summer. The first trip came weeks after the Cheonan sinking. The second time came just before North Korea's Worker's Party held a rare conclave and then a nationwide pageant for the elevation of Kim's son, Kim Jong Un, as dictator-in-waiting. Chinese Politburo member Zhou Yongkang stood with the elder Kim during the festivities.

The steadfastness of Beijing's support at the expense of its international image and relations with Seoul and Washington have raised criticisms even in China that the North Korean tail sometimes wags the Chinese dog. Chinese officials and experts acknowledge the risk, saying Beijing's leverage is limited, given that it is unwilling to throw its economic heft.

"Even if China tried to tell North Korea what to do, it's unlikely they would easily listen," said Gong Keyu, deputy director of the Asia-Pacific Research Center at Shanghai's Institute for International Studies.