The family of late pipeline billionaire George Lindemann has agreed to return 33 looted artifacts to Cambodia, according to the US Attorney's Office, a decision described as "momentous" by the Southeast Asian country.

The collection includes statues of deities, angels and demons from the 10th and 12th centuries from Koh Ker, the ancient capital of the Khmer kingdom, and from the famous Angkor Wat temple, the office said.

In a statement, it said the family's decision to return the artifacts was voluntary. Cambodia's archaeological sites suffered widespread looting during civil conflicts from the 1960s to 1990s and its government has spent years pursuing the return of the antiquities, some of which it says are on display in US museums.