Chinese President Xi Jinping's unusual warning to North Korea is seen as a sign that Beijing's strategic thinking on the problematic communist neighbor could change as its relations with South Korea grow stronger.

After summit talks with U.S. President Barack Obama, Xi told a joint news conference that China is committed to realizing the complete and verifiable denuclearization of the Korean Peninsula in peaceful way, a remark in line with China's long-running stance.

But then Xi went a step further and said, "We oppose any actions that might cause tension in the Korean Peninsula or violate U.S. Security Council resolution."

Xi did not mention North Korea by name, but the remark was a clear warning to Pyongyang not to go ahead with its threatened nuclear or missile tests that are banned under a series of U.N. Security Council resolutions.

It was highly unusual for a Chinese leader to publicly issue such a warning, given that Beijing has been reluctant to criticize North Korea and has usually urged all sides to exercise calm and restraint and resolve disputes through dialogue.

What was also unusual in Xi's remarks was the absence of a call for an early resumption of the long-stalled six-party talks on North Korea's nuclear program -- an appeal that has long been seen as efforts to back North Korea's call for unconditional resumption of nuclear negotiations.

Such changes raise hope that Beijing's thinking on North Korea may change.

China is North Korea's last remaining major ally and a key provider of food and fuel. But it has been reluctant to use its influence for fear that pushing the regime too hard could lead to its collapse, instability on its border and ultimately the emergence of a pro-U.S. nation next door.

That's why China has never gone as far as to cause real harm to the North even when it increased pressure and imposed sanctions on the neighbor, especially when Pyongyang defies international appeals and carries out nuclear tests and other provocative acts.

It was unclear what prompted Xi to break from practices and issue a warning to the North or if it represented a real change in China's strategic calculus with regard to the North.

But the changes came as China's relations with the North have markedly soured while its ties with South Korea have significantly strengthened in recent years.

The Beijing-Pyongyang relations took a nosedive after North Korea defiantly carried out its third nuclear test in early 2013, a few months after Xi took office. Analysts have said that Xi is believed to have taken the test as an affront to him.

Xi's displeasure with the North has been apparent.

Breaking from decades of tradition, Xi visited South Korea in 2014, becoming the first Chinese president to visit the South ahead of the North. Xi has not yet visited the North or met with its young leader, Kim Jong-un, although he held a series of summit meetings with South Korean President Park Geun-hye.

On the other hand, China's relations with the South have been significantly upgraded under Xi and Park. So much so that even concerns have arisen in the United States that Seoul may be tilting too much toward Beijing.

Early this month, Park attended China's massive military parade marking the end of World War II.

Her attendance not only symbolized the sea change in relations between South Korea and China, which fought on opposing sides in the 1950-53 Korean War, but it also underscored the deep strains in the traditional alliance between Pyongyang and Beijing.

Park's decision to attend the parade raised eyebrows among many U.S. experts and analysts as the event was seen as China's muscle flexing and was shunned by all Western leaders. But South Korea said it believes her attendance would be helpful in winning Chinese cooperation in resolving the North Korean nuclear issue.

Xi's unusual warning to the North on Friday could be an outcome from Park's attendance at the parade and more broadly, the ever-strengthening relations between Seoul and Beijing. (Yonhap)