Bombs are a key part of both offensive and defensive operations by Isil, which overran large parts of Iraq last year.
Explosives continue to pose a major threat even after the jihadists are gone and prevent displaced residents from returning home.
The grave, located about six miles west of Sinjar, has not yet been excavated, but the victims were not buried deeply, and some of their remains have been exposed by rainwater, added Mr Khalil.
Another mass grave found in the area was believed to hold the bodies of some 80 women aged from 40 to about 80, whom one official said may have been executed because they were considered too old to enslave and rape.
The town of Sinjar was recaptured from Isil on November 13 in a major
operation led by forces from Iraq's autonomous Kurdish region, backed by air support from the US-led coalition.