Roughly 600 North Korean troops have been killed fighting alongside Russia against Ukraine, South Korean lawmakers said on Wednesday, citing the country’s intelligence agency.

North Korea has suffered about 4,700 casualties in the conflict, which includes deaths and injuries. But some of the country’s troops have shown signs of improvement in combat capabilities over about six months by using modern weapons such as drones, the lawmakers said.

“After six months of participation in the war, the North Korean military has become less inept, and its combat capability has significantly improved as it becomes accustomed to using new weapons such as drones,” Lee Seong-kweun, a member of the parliamentary intelligence committee, told reporters, after being briefed by South Korea’s National Intelligence Service.

A total of about 15,000 North Korean troops have been deployed to fight Ukraine.

Russian President Vladimir Putin thanked North Korea for sending troops and promised not to forget their sacrifices. (Sputnik/Mikhail Metzel/Kremlin via Reuters/File Photo)

The two U.S. adversaries have moved significantly closer to each other in recent years.

Lee said the remains of dead North Korean soldiers were cremated in Kursk before being shipped back home.

North Korea is also believed to have sent about 15,000 workers to Russia, according to the lawmakers, citing intelligence assessments.

U.S. President Donald Trump said Saturday he doubts Putin wants to end the war. Just a day before, Trump had said Ukraine and Russia were “very close to a deal.”

Reuters contributed to this report.