Mexico has stepped up security in a troubled western region after a string of attacks on electricity installations over the weekend that temporarily knocked out power for hundreds of thousands of people.
Energy Minister Pedro Joaquin Coldwell told reporters security forces had increased their presence at facilities of the state-run electricity company the Federal Electricity Commission (CFE) and oil monopoly Pemex in the violent state of Michoacan.
An unspecified number of substations were attacked and damaged early on Sunday, and six gas stations were also damaged, Michoacan's interior minister, Jaime Mares, told Mexican radio on Monday.
Local media said blackouts affected more than 400,000 people across the mountainous state of some 4.4 million. Parts of Michoacan have fallen under the control of criminal gangs who are fighting among themselves and against authorities.
Mares declined to say who may have been behind the attacks in Michoacan, where clashes between the powerful Knights Templar drug cartel and rival gangs have sparked much violence.
Raul Benitez, a security expert at the National Autonomous University of Mexico (UNAM), said he believed the strikes had been carried out by the Knights Templar in retaliation for government efforts to crack down on the gang.
"It's a decision to carry out general terrorism," Benitez said. "And this will now lead to a very strong response by the government, backed by the population."
Petrol bombs were used in some of the attacks, which involved at least 19 CFE installations, local media said.
Mares said there were no deaths in the attacks, although local media reported that five suspected cartel henchmen were gunned down by vigilantes in the town of Aguililla near the city of Apatzingan, a stronghold of the Knights Templar.
Michoacan has been rocked by repeated explosions of civil unrest this year, and protesters have repeatedly blocked major streets and highways in the capital and other cities.
Compounding matters, vigilante groups have sprung up in the region this year which complain that state and federal police are not protecting them from the gangs.
President Enrique Pena Nieto in May sent a general to take over all police and military operations in the state.
Michoacan was where former President Felipe Calderon launched his military-led crackdown on drug cartels shortly after taking office at the end of 2006.
Though he succeeded in capturing or killing many capos, Calderon could not contain the violence between the gangs, which has since claimed about 80,000 lives.