Relations between North Korea and China have changed markedly due to Pyongyang's refusal to denuclearize and repeated provocations, South Korea's top nuclear envoy said Friday.

Hwang Joon-kook, special representative for Korean Peninsula peace and security affairs, cited China's attitude on the North in its recent military stand-off with the South.

"China won't side with North Korea over its provocative act," he said at a forum in Seoul to mark the 10th anniversary of the Sept. 19 Joint Statement.

Under the 2005 agreement, a result of the six-party nuclear talks, the North agreed to abandon its nuclear program in return for political and economic incentives from the South, the U.S., China, Japan and Russia.

But the document is now treated as a mere scrap of paper, with the talks deadlocked for nearly seven years.

Hwang warned the North not to throw cold water on the nascent dialogue mood amid reports that the unpredictable country may fire a long-range rocket or conduct another nuclear test around October.

The envoy said Beijing would not blindly patronize Pyongyang any more.

"Since President Xi Jinping took power, in particular, China-North Korea ties have been changing in quality because of the nuclear issue."

The latest inter-Korean military crisis has highlighted not only the strength of the South Korea-U.S. alliance but also a shift in North Korea-China relations, he added.

China used to blame both Koreas for tensions on the peninsula, including when the North launched a series of deadly attacks on the South in 2010.

China took a bit different stance this time, Hwang said, apparently putting more pressure on the North. (Yonhap)