SEOUL, South Korea — Russia has supplied air defense missile systems to North Korea in exchange for sending its troops to support Russia’s war efforts against Ukraine, a top South Korean official

said Friday.

The U.S., South Korea and Ukraine say North Korea sent more than 10,000 troops to Russia in October, some of whom have recently begun engaging in combat on the front lines. North Korea’s troop deployment threatens to escalate the war, and what Russia could give to the North in return has been a source of rampant international speculation.

The most alarming development for South Korea and the U.S. would be Russia transferring sophisticated weapons technology that can enhance North Korea’s nuclear-capable missiles targeting its rivals. Many experts say, though, that it is unlikely Russia would do this in the initial stage of the North’s troop deployment.

Shin Wonsik, national security adviser for South Korean President Yoon Suk Yeol, told an SBS TV program Friday that South Korea has found Russia provided missiles and other equipment to help it reinforce its air defense network for Pyongyang, the capital. Shin didn’t say what specific missiles Russia gave to North Korea.

Lee Illwoo, an expert with the Korea Defense Network in South Korea, said that Russia has likely sent S-400 long-range surface-to-air missiles, launchers and ground-based radar systems. He said that North Korea is capable of building shorter-range surface-to-air missiles on its own.

The S-400 missile, with a range of 250 miles, is considered one of Russia’s most advanced anti-aircraft weapons. But Lee questioned how significantly it can boost Pyongyang’s air defense, saying Russian air defense systems have failed to effectively deal with Ukrainian drone assaults.