The FBI is investigating an apparent attempt to firebomb a fast-food restaurant in Reno where authorities reported a window was broken, a flammable liquid found inside and the initials of an animal rights group scrawled on a drive-thru sign.

The bureau began investigating after the incident was discovered Monday, FBI spokeswoman Bridget Pappas in Las Vegas said Tuesday.

KOLO-TV, the ABC affiliate in Reno, first reported (http://bit.ly/1xaCtuy ) that the damage — including "ALF" spray-painted on the sign — was discovered by KFC employees arriving for work at the store northeast of downtown.

Animal Liberation Front activists have long accused KFC of animal cruelty. The group most recently claimed responsibility for a fire in February 2014 that badly damaged a KFC in Upper Hutt, New Zealand.

Nicoal Sheen, a national press officer for the North American Animal Liberation Press Office in Los Angeles, said Tuesday that the group is not aware of anyone claiming responsibility for the incident in Reno. "We have not received any anonymous communique on this," she told The Associated Press.

No one was hurt, and the Reno restaurant suffered only minor damage. The writing on the sign had been removed by Tuesday, but the drive-thru remained closed.

Another animal rights group, People for the Ethical Treatment of Animals, picketed in front of a Reno KFC in 2003 in protest of the restaurant chain's refusal to change the way it treats and kills chickens.

The most recent violence in Reno that the Animal Liberation Front claimed responsibility for was a fire in May 2009 that gutted the business office of a company that ships monkeys from China for scientific research in the United States and elsewhere.

In 2007, several members of a cell group of the Animal Liberation Front were convicted of setting more than 20 fires in five Western states that did a total of $40 million in damage, including an arson fire in 2001 at a U.S. Bureau of Land Management facility housing wild horses in Litchfield, California — about 90 miles northwest of Reno.

Reno police spokesman Officer Tim Broadway said Tuesday there have been no new developments in the May 2009 case. He said he couldn't comment on the latest incident involving KFC because the FBI is handling the investigation.

Pappas said she could not say why the FBI is involved.

"We don't have any additional details at this time," Pappas told AP. "And because it is an ongoing investigation, we won't be commenting."

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Ken Ritter reported from Las Vegas.