The site of a castle from the ancient Korean kingdom of Balhae, almost the size of the kingdom's capital, has been discovered in Siberia.

The state-run National Research Institute of Cultural Heritage on Thursday said it found numerous artifacts and remains from the Balhae Kingdom that ruled the northern Korean Peninsula as well as eastern China and southern Russia between AD 698 and 926.

Korea has been conducting a three-year-long joint archaeological survey with Russia since September.

The research center said the total size of the area discovered covers 160-thousand square meters, the largest Balhae Kingdom castle site ever to be found in the Siberian region so far.