MEXICO CITY (Reuters) - Twelve people were killed in shootings in the central Mexican state of Puebla in violence linked to warring gangs of fuel thieves, the state attorney general’s office said on Tuesday, adding to a mounting death toll from the lucrative trade.

Illegal fuel taps and gasoline thefts cost Mexico hundreds of millions of dollars each year.

Fighting between the fuel thieves, known as huachicoleros, has this year helped push violence in Mexico to its highest levels since President Enrique Pena Nieto took office at the end of 2012.

Authorities found the bodies of four men and a woman in the state capital, also named Puebla, after they were attacked by unidentified gunmen, state prosecutors said in a statement.

The bodies of two men were also found in the municipality of Amozoc de Mota just east of the capital, prosecutors said.

In addition, five others were killed in a shootout between suspected fuel thieves in Tlaltenango on the northwestern fringe of the city of Puebla, state prosecutors said.

All twelve deaths are believed to be the product of disputes between gangs of fuel thieves, and all occurred on Monday, a spokesman for the attorney general’s office said.