MEXICO CITY -- Prosecutors in western Mexico said Friday they have found the badly decomposed remains of 16 men and three women in clandestine burial pits.

An official of the Jalisco state government who was not authorized to be quoted by name said the bodies were found during excavations starting earlier this week.

The pits were detected near the city of Lagos de Moreno after neighbours reported foul odours coming from a vacant lot.

Drug and kidnapping gangs in Mexico frequently use such mass graves to dispose of the bodies of victims and rivals.

Earlier this week, prosecutors in Jalisco said they were also investigating the killing of five homeless people in the capital of Guadalajara.

The state prosecutor's office said in a statement Wednesday that authorities are examining whether a single killer was "possibly" involved.

"The victims were attacked while they were sleeping and defenceless," the office said. "The weapon used was a rock weighing over 11 pounds (5 kilograms), the injuries were traumatic wounds to the skull."

The office said investigators are looking for a suspect who could have carried out the attacks between midnight and 5 a.m. and was strong enough to repeatedly lift and throw such a rock.