Mexican police found 10 decapitated corpses and 11 heads in a southwestern state that has become a major problem for President Enrique Pena Nieto since the apparent massacre of 43 trainee teachers there in September.
Several of the headless corpses found in graves about 50 kilometers (31 miles) east of the Guerrero state capital Chilpancingo showed signs of torture and had their hands tied, local security officials said on Wednesday.
The 11 severed heads were discovered in one grave, inside four black plastic bags, the Guerrero state prosecutor's office said in a statement. The identity of the victims was unclear.
Mexico's government is still investigating what happened to the missing students, who it says were abducted on the night of Sept. 26 by corrupt police in league with a drug gang in Iguala, the third biggest city in Guerrero.
Attorney General Jesus Murillo said the evidence strongly suggested that police officers handed the students over to drug cartel members who incinerated them. The remains of only one of the missing 43 has been identified so far.
The fate of the students has sparked major street protests in Mexico, and Pena Nieto has come under pressure to clear up the case and put an end to drug violence in the country.
In a meeting with Pena Nieto at the White House on Tuesday, President Barack Obama said he was committed to helping Mexico eradicate the cartels, but that it was up to the Mexican government to resolve the problem.