SEOUL - North Korea's military provocations this year angered its ally China but Beijing remains reluctant to tighten the screws on Pyongyang, an influential think-tank said Tuesday.

China is more concerned about its neighbour's stability than its nuclear programme and views the nuclear issue as mainly the responsibility of the United States, the Brussels-based International Crisis Group (ICG) said in a report.

The North's April rocket launch and withdrawal from six-party nuclear disarmament talks, and its nuclear test in May, coincided with reports that leader Kim Jong-Il may be seriously ill.

"Together, the nuclear tensions and succession worries drew out an unusually public, and critical, discussion in China about its ties with North Korea," the report said.

Beijing backed new United Nations sanctions against Pyongyang but its strategic calculations remain unchanged, the ICG said. It would continue to shield its neighbour from the effect of stronger sanctions.

"China prioritises stability over denuclearisation due to a vastly different perception than the US and its allies of the threat posed by a nuclear North Korea," the report said.

Its greatest concerns were a possible military confrontation between North Korea and the US, regime collapse, a flood of hundreds of thousands of North Korean refugees into China, or "precipitous reunification" with South Korea leading to a US military presence north of the 38th parallel.

In order to limit the damage that sanctions might do to Kim's regime "it remains reluctant to tighten the screws on Pyongyang."

While the North's "dangerous brinkmanship" had sparked a continuing policy debate, China overall remained averse to any move which might destabilise a border state.

"Beijing therefore views the nuclear issue as a longer-term endeavour for which the US is principally responsible, and continues to strengthen its bilateral relationship with North Korea," the ICG said.

China does not want North Korea to have nuclear weapons, said Robert Templer, the ICG's Asia programme director, in a statement.

"But it is willing to go only so far in applying pressure, as it wants instability on its periphery even less."

The North Monday repeated its call for direct talks with the United States to end the nuclear standoff, and said successful bilateral talks could lead to a resumption of the six-nation negotiations chaired by China.

The US State Department said it was still considering whether to hold talks.