Envelopes containing a suspicious white powder were mailed to two LDS temples and a Catholic fraternity, prompting a hazardous materials response and a federal investigation into who is behind it.

The white powder scares were reported Thursday at Salt Lake City's Temple Square, the LDS Church's temple in Los Angeles and at a printing plant belonging to the Knights of Columbus in New Haven, Conn.

"Our mailroom employees discovered an envelope that had been mailed to us from California shortly before noon," Pat Korten, vice president of communications for the Knights of Columbus, told the Deseret News late Thursday. "When they opened it some white powder escaped."

The Church of Jesus Christ of Latter-day Saints and the Knights of Columbus are both major backers of the controversial Proposition 8, which banned same-sex marriage in California. However, the FBI cautioned late Thursday there is no evidence to link the threats to Prop. 8 opponents.

"We've got to follow the evidence and at this point we have not received anything that would lead us to believe the opponents of Prop. 8 are behind any kind of terroristic activity," FBI Special Agent Juan Becerra said from the agency's Salt Lake City office. "It would be irresponsible to say that at this point."

LDS Church security officials called Salt Lake police and firefighters about 4 p.m. Thursday when an employee in the recorder's office inside the Salt Lake Temple annex opened a manila envelope.

"When the employee opened it up and looked inside it, there was actually another white envelope inside that had a white powdery substance in it," Salt Lake Fire spokesman Scott Freitag said.

The employee who opened it immediately set the envelope down and called church security officials, who came over wearing a respirator and plastic gloves. They sealed the envelope inside a plastic bag, Freitag said.

Three employees in the room at the time were quarantined. Security denied access to the room and shut off the air vents.

"They are not complaining of any injury or illness," Freitag said, adding that they did not have to undergo a decontamination process.

Hazardous materials teams sanitized the substance to ensure it was not a biological agent like anthrax.

On the Main Street plaza, missionaries and other church employees were allowed to come and go. A lone LDS security official stood behind the temple gates. He opened the gate for firefighters, then closed and locked it behind them.

A pair of FBI agents left Temple Square with the envelope in a black plastic bag. The envelope was taken to a lab to be tested.

"We are working to find out what it is and hopefully it's harmless," Becerra told the Deseret News.