Four severed heads found in Guatemala City
Four severed heads and two beheaded bodies have been found in the capital of Guatemala.
The bodies were left in the open around Guatemala City, including in front of Congress and at a shopping centre.
Messages to the interior minister and the director of prisons were pinned to them, leading police to blame drug gangs for the killings.
So far only two bodies have been found and none of the victims have been identified.
Interior Minister Carlos Menocal said the first head was found in front of Congress, the second at a shopping centre, another in front of a fire station and the fourth in a residential neighbourhood.
Police spokesman Donald Gonzalez said the killings were linked to drugs, and came after a string of arrests of alleged high-profile drug traffickers.
"They [the killers] left them in strategic places where there's a lot of foot traffic so everyone could see them," Mr Gonzalez said.
He said he believed the killings were in revenge for new restrictions imposed in the country's prison system.
One of the messages read "no more impunity".
Earlier this year Guatemala introduced stricter prison rules, including more frequent transfers to different jails, to prevent convicts from continuing to run criminal enterprises from behind bars.Revenge killings?
Interior Minister Carlos Menocal read out one of the messages, which had been written on cardboard and propped up against the remains.
"This is happening because of the mistreatment and the injustices in the country's jails," the message read.
"If you don't do anything about these mistreatments, what happens from now on will be the fault of the government and the prison system, who are the ones abusing their authority."
The killings come three days after the resignation of the director of a United Nations-backed commission to combat links between organised crime and the Guatemalan state.
Carlos Castresana stepped down saying that the Guatemalan government had not kept its promise to reform the justice system.
He also urged President Alvaro Colom to sack the recently-appointed prosecutor general, who he accused of having links with criminal gangs.
Mr Gonzalez, the police spokesman, said criminal gangs were taking advantage of a vacuum left by Mr Castresana's resignation "to wreak havoc".
Decapitation is used by Mexican drug gangs to spread fear among their rivals and the security forces but has not yet widely spread from Mexico.
But one of Mexico's most powerful and violent drug cartels, Los Zetas, is believed to be active in Guatemala, and a number of violent shoot-outs in 2008 were attributed to them.
Guatemala is seen as an ideal transit point for cocaine smuggled from Colombia through Guatemala to Mexico and on to the US.