* Suspected drug gang members arrested
* Authorities investigating extortion as possible motive
MEXICO CITY, May 29 (Reuters) - Mexican police are beefing up patrols around warehouses belonging to PepsiCo's local snack food company Sabritas following a series of arson fires that damaged five of the firm's installations, an official said on Tuesday.
Federal and state police are patrolling three of the warehouses damaged in attacks this past weekend in the western state of Michoacan, Julio Hernandez, a spokesman for the state government, said in a telephone interview.
Installations in three other cities that were not targeted are also under police surveillance, he said.
Investigators are still probing the motive of the attacks, but authorities in the central state of Guanajuato on Monday said they have arrested four suspects linked to a drug gang for the fires set at two warehouses in that state.
"There were apparently a lot more people involved," Hernandez said. "Prosecutors are following various lines of investigation, one of which is extortion."
The attacks appeared to be the first to hit a global brand during Mexico's bloody war on drug cartels. No one was injured in the fires that destroyed trucks and damaged warehouses, authorities said.
Mexico, Latin America's second-biggest economy, has continued to attract foreign investment even as the country's drug war escalated since 2006. But global firms have favored states with lower levels of violence.
"Our investments from foreigners have fallen practically to zero," Michoacan's Hernandez said.
Gangs have extorted businesses, but Cesar Mendoza, Sabritas legal director, told local radio that he had no knowledge of any extortion threats against the company.
"We have filed criminal complaints with all the facts that we have and it will be the responsibility of the authorities to determine who is responsible," Mendoza said in an interview with Radio Formula.
He said the company was still calculating the cost of damage from the fires.
PepsiCo earned $4.8 billion, or 7 percent of its global net revenue in 2011, in Mexico, one of its top foreign operations.
Authorities in Guanajuato said the four suspects arrested for the attacks are all allegedly members of Los Caballeros Templarios gang (Knights Templar), an offshoot of the La Familia cartel that is fighting for territory in the west of Mexico.
Around 55,000 people have died in drug-related violence since Mexican President Felipe Calderon took power in December 2006 and launched a military crackdown on cartels.