Police in Mexico have found nine decapitated bodies close to a highway in the southern state of Guerrero.
Local officials said the victims were a policeman and eight soldiers.
Nine heads were found earlier in plastic bags close to a supermarket, reportedly with a note warning of more decapitations to follow.
Nearly 5,400 people have been murdered in drugs-related violence this year. Thousands of troops have been deployed across Mexico to tackle drugs gangs.
Local media reported that the soldiers were believed to have been abducted on Saturday as they left a nearby military base, close to the city of Chilpancingo.
Another three decapitated bodies were found on Sunday on the outskirts of the city, officials said.
President Felipe Calderon has deployed about 40,000 troops and police since December 2006 against the drugs cartels.
However, Mexico's top prosecutor has said that the violence is likely to worsen in 2009 as drug gangs split and fight for turf.
Officials say the increasingly gruesome nature of the violence shows that the drugs gangs are being squeezed, intensifying their internal squabbles.
In a statement, the defence ministry said the murders of the soldiers were the result of "the severe blows the Mexican army and air force have dealt to organised crime" and described the drug gangs as "cowards" who had been "cornered and weakened".
But the latest killings suggest the drug traffickers are prepared to take on the security forces, says the BBC's Stephen Gibbs In Mexico City.
The gruesome tactic of decapitation would appear to be designed to spread fear among anyone who threatens them, he says.
Local media reported that a message was found next to the nine heads warning, "For each one of us they kill, we'll kill 10 of them."