A federal grand jury has indicted four officials at a Northern California slaughterhouse at the center of a massive beef recall, alleging they slaughtered cows with cancer while inspectors were on their lunch breaks and distributed the diseased cattle, prosecutors announced Monday.

Petaluma-based Rancho Feeding Corp. halted operations in February after a series of recalls, including one for 8.7 million pounds of beef. The meat was sold at Walmart and other national chains and used in products, including Hot Pockets.

The U.S. Department of Agriculture has said Rancho processed diseased and unhealthy animals and circumvented federal inspection rules.

Slaughterhouse co-owners Jesse Amaral Jr. and Robert Singleton and employees Eugene Corda and Felix Cabrera were charged with distribution of adulterated, misbranded and uninspected meat.

Prosecutors said Cabrera and Corda were involved in the slaughter of cows with skin cancer of the eye at Amaral and Singleton's instructions. They are accused of then concealing the diseased heads by swapping them with healthy cow heads.

Cabrera, based on instructions from Amaral, also directed Rancho employees to carve stamps condemning cattle out of carcasses and to process them for transport and sale, prosecutors said. The indictment accused the company of distributing 179 diseased cattle.

It was not immediately clear whether the men had attorneys.

There have been no reports of illnesses linked to the products, which were processed from Jan. 1, 2013, through Jan. 7, 2014, and shipped to distribution centers and retail stores in California, Florida, Illinois and Texas.

More than 1,600 food distributors in the United States and Canada were alerted to the recall that asked consumers to return products, including beef jerky, taquitos, hamburger patties and Hot Pockets frozen sandwiches.

In March, the USDA allowed another Northern California company, Marin Sun Farms, to take over the shuttered Rancho slaughterhouse.

—The Associated Press contributed