SEOUL, South Korea (AP) -- Russia has supplied anti-air missiles to North Korea in exchange for it sending troops, a top South Korean official said Friday.

The U.S., South Korea and others say North Korea has sent more than 10,000 troops to Russia to support its war against Ukraine. What Russia would give North Korea in return has been the focus of keen attention.

National Security Director Shin Wonsik told a SBS TV program Friday that South Korea has found Russia has provided anti-air missiles and other equipment to reinforce its air defense network for Pyongyang, the capital.

Shin says Russia has also give diverse economic assistance to North Korea.

Seoul and Washington have voiced worries about possible Russian transfers of sensitive nuclear and missile technology to North Korea.

South Korea's spy agency told lawmakers Wednesday that North Korea had recently sent additional artillery systems to Russia as well. Last month, the National Intelligence Service said that North Korea had sent more than 13,000 containers of artillery, missiles and other conventional arms to Russia since August 2023 to replenish its dwindling weapons stockpiles.

Earlier this week, North Korea and Russia reached a new agreement for expanding economic cooperation following high-level talks in Pyongyang this week, according to the countries' state-run media.