The Hanoitimes - Stone tools dating back as far as 20,000 years have been found in three caves in the northern province of Thai Nguyen.

According to Professor Trinh Nang Chung, head of the excavation team, the discovery widens scientists' knowledge of prehistoric culture in the area. All three sites are being excavated further.

Among the three caves, Kim Son Cave in Vo Nhai District, which locates near Nguom Cave – already a noted archaeological site – is the most important.

In the second site, Thung Cave in Phu Luong District, a 50cm layer of earth contained stone tools, broken ceramic pieces, animal teeth and well-polished metal hatchets.

Professor Chung said decorative patterns o­n ceramic wares found at the cave had features of the Phung Nguyen culture of 4,000-3,500 years ago.

In another cave, named Than in Dong Hy District, a thick layer of coal ashes were found together with tools made from animal bones. Than Cave is thought to have been used as recently as 4,000 years ago.