MORELIA, MEXICO (AFP) - A chilling note was found alongside the severed heads and dismembered bodies of four people on Thursday in the Mexican state of Michoacan, where vigilantes are battling a drug cartel.

The heads were placed on top of plastic bags on a street in the town of Zacapu, an official in the Michoacan state prosecutor's office told AFP. The arms and legs were found near a church. A note was left near the body parts, reading: "This is what will happen to those who support the Knights Templar" cartel.

The victims have been identified, and the authorities are trying to determine whether they are linked to organised crime.

In another gruesome discovery, the prosecutor's office said it dug up the bones of two humans in the town of Tancitaro. Last weekend, two decapitated heads were left in the town of Antunez.

The Knights Templar have been locked in a turf war with the Jalisco New Generation drug cartel. Last year, civilians fed up with the police's failure to deal with the Knights Templar gang began to form vigilante militias to oust the criminals from the region.

The government of President Enrique Pena Nieto has deployed thousands of federal police and troops to Michoacan, seeking to restore security, but violence has continued. Shortly after reinforcements were sent in January, assailants set fire to and looted five shops in the neighbouring states of Hidalgo and Mexico State.

The federal authorities announced on Thursday the arrest of 19 suspected members of a criminal organisation, which they did not identify, in connection with the Jan 19 arson attacks. Nine were detained in Michoacan and 10 in Mexico State. Eight large firearms, seven smaller guns and books referring to a criminal group that operates in Michoacan were seized.