The confrontations late Wednesday in the central state of Puebla marked an escalation of recent conflicts in which fuel thieves have largely taken control of some towns in the so- called "Red Triangle" area east of Mexico City.
The Defence Department said attackers hiding behind a group of women and children killed two soldiers and wounded a third in the initial confrontation.
"In light of this situation, the soldiers decided not to return fire because the attackers were using women and children as a human shield," the department said in a statement yesterday.
Hours later, gunmen again attacked the patrol with armoured cars and high-powered rifles, killing two more soldiers and wounding nine, while three attackers were killed, according to the military, which said the assailants used five vehicles, three of them armoured.
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Puebla state officials said later that another three attackers had died.
Angry residents of Palmarito set up road blocks yesterday to protest of the army crackdown, demanding the release of some of the dozen residents detained in the clashes.
Federal Police said hours later that traffic had been restored in both directions along the toll highway between the cities of Puebla and Cordoba.
But it is the pipeline thefts -- thousands of illegal taps drilled into state-owned pipelines every year -- where local populations have been recruited en masse by gangs that often distribute drugs, steal gasoline and diesel and carry out extortion and kidnapping. They are known in Mexico as "huachicoleros," a term that refers to illegal or sub-par fuel sold from plastic tanks on roadsides.
While the government's Pemex oil company no longer releases official figures, 5,574 illegal pipeline taps were found in 2015. By some recent estimates, they cost the company about USD 1.5 billion per year in lost production.