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BEIJING, Oct 10 (Reuters) - China saidon Tuesday that North Korea's nuclear test had hurt ties between the communist neighbours and conspicuously declined to rule out backing possible U.N. sanctions aimed at Pyongyang.

Chinese Foreign Ministry spokesman Liu Jianchao told a regular news briefing in Beijing that war over North Korea's nuclear weapons was "unimaginable" and urged a return to the six-party talks.

But asked repeatedly about whether China stood by its long-standing opposition to sanctions against Pyongyang, Liu said "the U.N. Security Council should take appropriate action" and any steps should encourage peaceful resolution of the crisis.

"The DPRK ignored the opposition of the international community and brazenly conducted a nuclear test," he said, repeating unusually forceful language used by the Foreign Ministry on Monday, shortly after North Korea said it conducted the test.

"China resolutely opposes this," Liu said.

China is a neighbour and traditional Communist ally of North Korea, but it has denounced the nuclear test and demanded that Pyongyang, which it has long propped up with donations of food and fuel, stop any action that could make matters worse.

Liu said that despite their friendship, China had never in any way assisted North Korea's nuclear programme and always opposed the nuclearisation of the Korean peninsula.

The test came after several rounds of six-party talks, which China hosted between 2003 and 2005, aimed at persuading North Korea to dismantle its nuclear programmes.

Liu said it was too early to say the diplomatic efforts and China's own policy of engagement had failed.

"The facts have proven that the six-party talks are the best way to resolve the issue, so I think this is not a failure of China's diplomacy," Liu said. "On the contrary, we will stay on the track of talks."

Liu said China would continue to seek to develop ties with North Korea, but added that relations must be beneficial to regional peace and security. He said there had been no sign of atmospheric pollution from the test.

South Korea's Yonhap news agency said on Tuesday North Korea was willing to end its nuclear programme and return to six-party talks if Washington "reciprocates". The group comprises the two Koreas, China, Japan, Russia and the United States.

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