US President Joe Biden meets with China's President Xi Jinping on the sidelines of the APEC Summit in Lima, Peru, Saturday. (Reuters-Yonhap)

US President Joe Biden called Saturday for China to use its clout to prevent an escalation of Russia's war in Ukraine through the dispatch of more North Korean troops, while raising concerns over the possibility of Pyongyang engaging in provocations, a senior US official said Saturday.

National Security Adviser Jake Sullivan elaborated on the discussions that Biden and Chinese President Xi Jinping had during their talks on the margins of the Asia-Pacific Economic Cooperation summit in Lima, amid mounting concerns about broad security implications of a military alignment between Moscow and Pyongyang.

"(Biden) also pointed out (to Xi) that the PRC does have influence and capacity and should use it to try to prevent a further escalation or further expansion of the conflict through the introduction of even more DPRK forces," Sullivan told reporters in a press briefing.

PRC and DPRK stand for the official names of China and North Korea, the People's Republic of China and the Democratic People's Republic of Korea, respectively.

Biden stressed the North's troop deployment was a "deeply dangerous" development, the official said.

"President Biden really underscored his view that this is a deeply dangerous development both in Europe and on the Korean Peninsula, with deepening cooperation between Russia and the DPRK likely to enhance the possibility of provocative behavior by the DPRK," Sullivan said.

"Provocative behavior that we have warned about, whether it comes in the form of direct provocations against the ROK, or whether it comes in the form of something like further missile tests or even a seventh nuclear test, which is something that we remain constantly vigilant about." ROK stands for South Korea's official name, the Republic of Korea.

Seoul and Washington have said that North Korean troops, dispatched to Russia's western front-line Kursk region, have begun engaging in combat operations against Ukrainian forces despite criticism that their introduction onto the battlefield could broaden the war and affect security in Europe and the Indo-Pacific.

The troops' entry into combat came after Moscow and Pyongyang signed a "comprehensive strategic partnership" treaty in June, which calls for one party to provide military aid to the other in the event of an armed invasion -- a pledge that amounts to a revival of the two countries' Cold War-era military alliance.

During the summit, the Chinese president told Biden that China does not allow "conflict and turmoil" to happen on the Korean Peninsula, according to an English-language readout from Beijing's foreign ministry.

"(China) will not sit idly by when its strategic security and core interests are under threat," Xi was quoted as saying.

At the start of the summit, Biden renewed calls to keep Sino-US rivalry from veering into conflict, with the Chinese president stressing his opposition to "decoupling" between the world's two largest economies.

The summit came amid expectations that President-elect Donald Trump could take a hard-line stance on trade with China and other China-related issues once he takes office in January.

"How we're getting along together can impact the rest of the world, and our two countries cannot let any of this competition veer into conflict," Biden said according to a pool report from the White House press corps.

"That's our responsibility, and over the last four years I think we've proven it's possible to have this relationship," he added.

Xi underscored his "consistent" belief that a stable relationship between the US and China is "critical" not only to the interests of the Chinese and American peoples but also to the "future and destiny of the entire humanity."

But he cautioned against "decoupling" between the two major powers.

"In an age of a new round of flourishing sci-tech revolution and industrial transformation, neither decoupling nor supply-chain disruption is the solution. Only mutually beneficial cooperation can lead to common development," Xi was quoted by Beijing's foreign ministry as saying.

His remarks came amid concerns that trade friction between Washington and Beijing could further escalate if Trump makes good on his campaign pledge to impose a 60 percent tariff on Chinese goods.

Xi also said that "small yard, high fences" is not what a major country should pursue, referring to the Biden administration's approach that keeps tight restrictions on select key technologies while ensuring the normal flow of trade in other sectors.

"Only openness and sharing can advance the well-being of humanity," Xi said. "As two major countries, China and the United States should bear in mind the interests of the whole world, and inject more certainty and positive energy into the turbulent world."

The summit was expected to discuss North Korea's troop deployment to support Russia's war in Ukraine and its provocative activities as Washington has wanted China to play a constructive role in addressing a range of issues concerning the recalcitrant regime.

Saturday's meeting was the third in-person summit between Biden and Xi since Biden took office in January 2021. The presidents previously met on the margins of the Group of 20 summit in Bali in 2022 and on the margins of the APEC summit in California a year ago. (Yonhap)