Two men have been indicted by a federal grand jury in connection with a pair of mink farm raids.

The indictments unsealed Thursday against William James Viehl, 22, and Alex Jason Hall, 20, charge them with two counts of damage and interference with animal enterprises. Federal authorities said it is in connection with an August 2008 raid on a South Jordan farm, where 300 minks were released and slogans like "No More Mink, No More Murder" and "ALF: We Are Watching" were spray-painted on property there.

The indictment also accuses the pair of attempting to damage a mink farm in Hyrum in October.

"While we recognize and respect the strongly held beliefs of those who advocate for animal rights, when their actions cross over the line into criminal conduct, we are going to take aggressive action," U.S. Attorney for Utah Brett Tolman said Thursday.

Viehl was arrested by FBI agents in Layton on Thursday. Hall was arrested in Ogden. Both men are being held in the Salt Lake County Jail pending an appearance in U.S. District Court in Salt Lake City on this morning.

The Animal Liberation Front claimed responsibility for the South Jordan raid, crediting one of its "soldiers." Tolman refused to say if he believed the two were part of the ALF, a loosely knit collective of hard-core animal-rights activists. The FBI has branded the group a "domestic terrorist organization," but federal authorities also would not say if they considered Viehl and Hall "terrorists."

Still, FBI agents said they are preparing for a pushback with so-called "sympathy attacks," from those carrying out attacks in the name of the accused.

"We're going to be keenly aware if anything like that comes up here," said Tim Fuhrman, the special agent in charge of the FBI's Salt Lake City office. "They operate on cloak and dagger."

Jerry Vlasak, who acts as a spokesman for the ALF, said such actions are not uncommon.

"They're putting the wrong people in jail," Vlasak told the Deseret News on Thursday. "These are people who care about innocent beings being tortured and killed for rich folks making a fashion statement."

Federal prosecutors said the grand jury investigation is ongoing. Still unsolved is the September 2008 raid on a Kaysville mink farm that led to the release of 3,000 minks.

Last month, two animal-rights activists were subpoenaed to testify before the federal grand jury, sparking protests outside the federal courthouse over the secret proceedings.

One of the activists refused to testify and faces a contempt of court hearing later this month. Jordan Halliday told the Deseret News on Thursday that he knows both Viehl and Hall, but he "would not assume" they were involved in anything, and he suspects federal authorities may try to press them for information on others.

"At this point I feel it's a fishing expedition," Halliday said. "I don't think they have evidence on these people. They're trying to charge them to set a precedent in the animal rights community."

Vlasak claimed the indictments of two people — who were not the ones called before the grand jury — is payback.

"They bring in these two activists before the grand jury last month who refused to cooperate," he said. "Now they're trying Plan B."