BEIJING, Aug. 19 (Xinhua) -- A total of 26 suspects have been arrested and more than 600 cultural relics retrieved in a major tomb robbery case which involves stolen items dating back to as early as the seventh century.

The suspects are believed to have involved in the illegal excavation of tombs in Dulan, a county in northwest China's Qinghai Province, and activities such as the brokerage and sales of stolen goods, the Ministry of Public Security said Sunday.

Among the 646 retrieved items, 16 are classified as national grade-one cultural relics.

Experts believe that many of the items are of tremendous historical value as they show cultural exchanges and interactions between the East and the West during the early Tang Dynasty (618-907).

Police will increase their crackdown on cultural relics crimes to better protect the country's cultural heritage, the ministry said in a statement.

Once a hub on the ancient Silk Road, Dulan is home to more than 2,000 tombs dating back to the Tang Dynasty, where silk, gold, silver, bronze ware and other items have been unearthed since 1982.