MEXICO CITY –  Shootings erupted over the weekend in three Mexican cities where drug gangs are fighting turf battles, killing at least nine people and wounding six more, officials said Sunday.

Gunmen on motorcycles arrived at a bar in the resort city of Cuernavaca and opened fire, killing three young men and a 22-year-old woman, the Morelos state prosecutor's office said. The attack near midnight Saturday also injured four people, who were recovering in local hospitals under police guard, a common practice when officials consider victims' lives still in danger.

In the northern city of Fresnillo, a group of armed men shot three people dead Saturday afternoon outside a convenience store. Federal and local police launched a wide search in the city of about 230,000 people that sits on a main drug trafficking route, but the attackers were still at large, the Zacatecas state attorney general's office said in a statement.

In the northern industrial hub of Monterrey, attackers shot at a group standing outside a bar in the early hours of Sunday, killing two men and wounding two. The shooting came three days after two masked gunmen killed four people and wounded two others inside a bar in a nearby suburb. Authorities have not said whether the shooting were related, but the assailants in both attacks arrived in taxis.

The weekend bloodshed raised fears that drug cartel violence may stir up again in areas where authorities had already applauded a reduction in drug-related homicides.

Meanwhile, the gangs continue to plot new ways to take over corridors into the United States.

Authorities in the northern state of Coahuila said over the weekend that police detained nine boys, two young women and 12 men who had arrived from different cities in northern Mexico on behalf of the violent Zetas cartel seeking to seize control of a city near Monterrey from a rival gang. Police confiscated 17 high-caliber weapons and ammunition.

In his first state-of-the-nation address earlier this month, President Enrique Pena Nieto reported a significant drop in drug-related killings, citing Monterrey and Coahuila's capital, Torreon, as examples. Many experts have expressed skepticism about the statistics used by the president.

Violence in Monterrey and in Fresnillo stems from a fight between the Zetas and the Gulf cartels, which were allies until they fell out in 2010. Cuernavaca, a retreat for U.S. retirees and favorite weekend getaway for Mexico City residents, has seen drug gang shootings involving remnants of the Beltran Leyva cartel.

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Associated Press writer Porfirio Ibarra in Monterrey contributed to this report.

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Adriana Gomez Licon on Twitter: http://twitter.com/agomezlicon