Note: This story was last updated at 6:40 p.m. July 29.

Three Plowshares protesters who oppose nuclear weapons allegedly sneaked through four fences at the Y-12 National Security Complex before dawn Saturday and spray-painted messages and splashed human blood on the walls of a uranium storage building before they were detained by security guards, an activist said.

The three were identified by supporters as Michael R. Walli, 63, of Washington, D.C.; Megan Rice, 82, of New York; and Greg Boertje-Obed, 57, of Duluth, Minn.

They are now in the Blount County Corrections Facility, said Ellen Barfield, of Baltimore, Md., who said she is a longtime anti-war and anti-nuclear weapons activist and friend of the three detainees.

Federal spokesman Steven Wyatt wasn’t able to confirm the identity of those arrested, but he said they entered a high-security area on the west end of Y-12—the Protected Area—at about 4:30 a.m. Saturday, spray-painted a building there, and splashed a substance that appeared to be like blood on a wall.

It could be the first security breach of that area, Wyatt said.

“I don’t ever recall this happening before at Y-12,” he said.

Y-12 has been involved in nuclear weapons work for decades, enriching uranium for the first atomic bomb used in wartime and continuing to store and process uranium today.

Wyatt said the trio arrested Saturday could face federal trespassing charges, and there could be other charges as well.

He wasn’t able to give more information, including how long they were inside the high-security area, whether they hung banners, and how they entered the site. He also did not directly respond to a question on whether the plant’s existing security system worked as intended.

Wyatt said an investigation by the U.S. Department of Energy Inspector General is under way. Federal officials will have to determine what happened and “go from there,” he said.

Sensitive materials were never at risk, Wyatt said.

Barfield said Walli, Rice, and Boertje-Obed reportedly spray-painted four messages on the $549 million Highly Enriched Uranium Materials Facility, or HEUMF.

The messages read: “Woe to the empire of blood,” “The fruit of justice is peace,” “Work for peace, not war,” and “Plowshares pleases Isaiah,” Barfield said.

The activists—Walli, a Roman Catholic layman; Rice, a member of the Roman Catholic Sisters of the Holy Child Jesus; and Boertje-Obed, a member of Veterans for Peace—also hung two banners, Barfield said.

The banners gave the name of Saturday morning’s action, “Transform Now Plowshares,” and referenced a biblical passage: “Beat swords into plowshares, spears into pruning hooks.”

The National Nuclear Security Administration announced the start-up of the HEUMF in January 2010. It was the plant’s largest construction project in more than 40 years and consolidated enriched uranium storage into one building.

Y-12 says the enriched uranium stored there is used for maintaining the U.S. nuclear deterrent and as a fuel source for naval reactors. The material is also used for “down-blended” fuel for commercial, research, and medical isotope production reactors.

Now, there are plans to build a Uranium Processing Facility at Y-12, a building that could cost $6.5 billion and be the largest construction project in Tennessee history. Saturday’s protest was apparently aimed at least in part at those plans.

Statements forwarded by supporters, including an “indictment” of Y-12, said the activists were responding to federal plans to invest a total of $80 billion to sustain and modernize the nuclear weapons complex.

“The ongoing building and maintenance of Oak Ridge Y-12 constitute war crimes that can and should be investigated and prosecuted by judicial authorities at all levels,” the statements said. “We are required by international law to denounce and resist known crimes.”

Another statement said the activists went to Y-12 because their humanity “rejects the designs of nuclearism, empire, and war.”

Barfield said the protesters were non-violent and religiously motivated, and Saturday’s action could be the first by Plowshares at Y-12. She described Plowshares as a three-decade-old international movement of people who primarily oppose nuclear weapons.

“These are loving people who are trying to urge humanity to disarm from the horrendous death-dealing that nuclear weapons are,” Barfield said.

The activists do not alert others to their plans beforehand in order to avoid conspiracy charges.

Barfield has been able to talk to the three since their arrests, and she said they could face vandalism charges as well. They are due in court Monday at the Federal Building in Knoxville, she said in a Sunday e-mail.

Asked about the blood that was reportedly used, Barfield said it is a very common Plowshares symbol, symbolizing the “horrendous violence of nuclear weapons and also the beautiful, quintessential symbol of life.”

Ralph Hutchison, coordinator of the Oak Ridge Environmental Peace Alliance, said Saturday’s protest had no connection to his nonprofit organization, which has a series of annual events planned early next month around the anniversaries of the bombings of Hiroshima and Nagasaki, Japan, on Aug. 6 and Aug. 9, 1945. Y-12 enriched uranium for Little Boy, which was dropped on Hiroshima near the end of World War II and was the first atomic bomb ever used in war.

The OREPA events, which also emphasize nonviolence, include a vigil, protest against the UPF, and peace lantern and remembrance ceremonies.