South Korea’s national security adviser Shin Won-sik told local broadcaster SBS that Russia has given North Korea equipment to improve its air defense systems in exchange for the more than 10,000 troops Pyongyang provided.

“It is understood that North Korea has been provided with related equipment and anti-aircraft missiles to strengthen Pyongyang’s weak air defense system,” Shin said, according to Reuters.

The North Koreans provided Russia with more than 10,000 soldiers earlier this fall, making them the first country to provide troops to either side of the conflict. Several NATO and non-NATO countries have provided Ukraine with military aid, while Iran and North Korea are the countries that have come to Russia’s aid.

“It’s certainly a possibility” that North Korea could provide Russia with more troops, Pentagon Deputy Spokeswoman Sabrina Singh said this week.

U.S. officials have said the North Korean troops are fighting Ukrainians in the Kursk region of Russia, where Ukrainian troops are currently occupying Russian territory.

In the aftermath of North Korea’s entrance into the war, the U.S. lifted restrictions it had placed on how Ukraine uses the weapons it provides. Specifically, Ukrainian forces are now allowed to use U.S.-provided long-range missiles to hit military targets deeper within Russian territory. The U.S. also provided Ukraine with anti-personnel landmines, which they hadn’t given them previously.

President-elect Donald Trump has said he will bring both sides to the negotiating table, seeking an end to the conflict. With his inauguration only weeks away, both sides are trying to make strategic gains quickly to improve their bargaining positions.

North Korean leader Kim Jong-Un and Russian leader Vladimir Putin have strengthened their relationship over the course of the war. Kim has not shown an interest in restarting talks with Trump.

“We have already gone as far as we could through negotiations with the U.S., and what we have confirmed at the end was not the willingness of a superpower to coexist but its uncompromising stance of strength and its unchangeable invasive and hostile North Korea policy,” Kim said in a speech, according to a state media released Friday.