The United States confirmed Tuesday that North Korean troops, who have been deployed to Russia's western front-line Kursk region, have begun engaging in combat operations against Ukrainian forces.

Vedant Patel, principal deputy spokesperson for the State Department, made the remarks amid growing concerns that the North's troop deployment could expand Moscow's protracted war in Ukraine with security implications for both Europe and the Indo-Pacific region.

"We are incredibly concerned by Russia's decision to turn to the DPRK to supply soldiers to continue their brutal war against Ukraine," Patel told a press briefing.

"Today, I can confirm that over 10,000 DPRK soldiers have been sent to eastern Russia, and most of them have moved to far western Kursk Oblast, where they have begun engaging in combat operations with Russian forces," he added.

Patel noted that Russian forces have been training North Korean troops in artillery, unmanned aerial vehicle (UAV) and basic infantry operations, including trench clearing operations, which he said are "critical" skills for frontline operations.

But he stressed that Russia's battlefield success using North Korean troops will in large part be dictated by how well Russia can integrate them into their military.

"Some of the challenges they would need to overcome are interoperability, the language barrier, command and control and communications," Patel said. "The United States is consulting closely with our allies and partners in other countries in the region on the implications of this, on these developments."

The North's troop deployment will likely be a topic to be discussed when Secretary of State Antony Blinken is in Brussels on Tuesday and Wednesday to discuss support for Ukraine with his counterparts at the North Atlantic Treaty Organization and European Union, according to Patel.

The US confirmation on the North Korean troops' entry into combat came as North Korean leader Kim Jong-un finalized the domestic ratification procedure for the "comprehensive strategic partnership" treaty with Russia in a telltale sign of deepening military cooperation between the two countries.

Kim and Russian President Vladimir Putin signed the treaty during their summit in Pyongyang in June. The treaty includes a mutual defense clause in what is seen as a revival of the two countries' Cold War-era military alliance. (Yonhap)