The site at Mekha Sanda near Mardan is located atop a hillock, 11 km away from the area where famous Ashoka inscription rocks are situated, local daily 'Dawn' reported today.
It quoted local residents as saying that the culprits secretly excavated the site some days ago and ruined the walls of remains.
The paper said the unidentified people took away a number of relics, including statues, pottery items and iron tools.
It said no one is posted to look after the site, which has been frequently excavated by the locals and smugglers.
Illegal excavations at all the sites has been going on without any check for quite some time amd extremely rare antiquities belonging to Greeko-Bactrian, Gandhara, Hindu Shahi, Kushan and early Muslim periods have been stolen from them, the report said.