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MEXICO CITY (Reuters) - At least four soldiers and six suspected oil thieves died in a battle in the central Mexican state of Puebla, authorities said on Thursday, as the army launched a major operation against organized criminals who siphon fuel from pipelines.

Some 600 soldiers were involved in the initial operation, the state government said, with another 400 backed by helicopters and truck-mounted weapons joining them.

The troops were called in to investigate a report of an oil pipeline theft at around 8:15 p.m. local time (0115 GMT) on Wednesday, near the village of Palmarito, when they were shot at by a group using women and children as human shields, the army said in a statement.

The soldiers decided not to return fire, but two of them died in the attack and another was wounded.

A few hours later in the same location, armed men in five sport-utility vehicles opened fire on a different group of soldiers, the army said in a statement on Thursday.

Two more soldiers died in the ensuing firefight and nine were wounded, the army said. Six suspected fuel thieves were killed, while one was wounded, it added. The army said soldiers also arrested at least 12 people, including two minors.

Television images on Thursday showed locals blocking a nearby highway with burning tires and a semi truck in the wake of the attacks. Local media reported that the protesters blamed the army for starting the incidents, and said a number of minors were still missing.

The clash is the latest chapter in a growing problem for the Mexican government. State-run oil company Pemex [PEMX.UL] says it is losing a record 27,000 barrels per day of gasoline and diesel as criminal gangs have become more involved in oil theft.