NUEVA ITALIA, Mexico (AP) — Gunfire erupted in a western Mexico town Sunday as hundreds of vigilantes pressed their fight over territory with a drug cartel, and Mexico's top security officials prepared to make yet another effort to try to stop the violence.

Members of so-called self-defense groups entered Nueva Italia in Michoacan state on a campaign they say is meant to liberate towns from the control of the Knights Templar cartel. Opponents and critics say the vigilantes are backed by a rival cartel, something the groups vehemently deny.

State Gov. Fausto Vallejo gave a brief statement Sunday saying he had formally asked the federal government for more help to quell the violence. He announced a meeting Monday in the capital to lay out a strategy to reclaim the peace.

Hundreds of vigilantes drove into Nueva Italia late Sunday morning in a caravan of large trucks, then surrounded the city hall and disarmed local police. An Associated Press journalist witnessed citizens initially welcoming them.

But shooting broke out almost immediately in and around the center square. Only one injury was reported by mid-day.

Gunfire could be heard around the city. Vallejo acknowledged violence has gone on for four days as vigilantes appeared to be advancing and surrounding the farming hub of Apatzingan, which is said to be the Knights Templar's central command.

Vallejo said he formally asked Interior Minister Miguel Angel Osorio Chong on Friday for more federal forces, "given insufficient state and municipal police."

The self-defense groups claim local and state police are in the employ of the Knights Templar.

Fighting between vigilantes and alleged cartel members has racked Michoacan for almost a year. President Enrique Pena Nieto's government already has sent thousands of federal police officers and soldiers to the state, but the situation has only worsened.

Both federal police and soldiers were seen near Nueva Italia on Sunday, but didn't intervene in the fighting.

Authorities reported finding a burned cargo truck and the bodies of two men hanging from a bridge in the area around Nueva Italia.

The federal government has said the civilian vigilante groups are operating outside the law. They carry high-caliber weapons that Mexico only allows for military use. But government forces have not moved against them and in some cases seem to be working in concert with the vigilantes.

Rumors circulate that some self-defense groups have been infiltrated by the New Generation cartel, which is reportedly fighting a turf war with the Knights Templar in the rich farming state that is a major exporter of limes, avocados and mangos.

Some in the region say members of the Knights Templar have also tried to use self-defense groups as cover for illegal activities.

The U.S. State Department issued a travel warning for Mexico on Thursday, recommending against travel in Michoacan, with the exception of the state capital, Morelia, and the port city of Lazaro Cardenas, and in those cases only by air.

"In many areas of the state, self-defense groups operate independently of the government ... are suspicious of outsiders and should be considered volatile and unpredictable," the statement said.

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Associated Press writer Gustavo Ruiz in Morelia contributed to this report.