The Federal Bureau of Investigation said a preliminary test result rules out known harmful substances, but spokesman Juan Becerra said that does not necessarily mean the powder was completely safe.

"Further tests will tell us what it is, or if it's something new," Becerra said Friday. "In no way, shape or form does this mean it's all clear. So far it's all fine, but we still need to test this further."

Becerra said full results would come sometime next week. Meanwhile, an investigation into the Salt Lake City incident, which mirrored a case at the Los Angeles Temple, will continue in concert with local, state and federal partners, according to an FBI news release.

Becerra said he does not know whether there was a return address on the envelope in which the powder was delivered, where the package came from or whether there was a note or threat attached to the materials.

The FBI also issued a reminder that sending the white powder will be prosecuted as "making false and misleading threats or attempts to use or threaten use of a weapon of mass destruction to promote public fear."

"Not only can they be prosecuted," Becerra said, "they will be."

At 4:05 p.m. Thursday, a recorder's office employee working in the temple's annex opened a manila envelope that contained a smaller envelope with powder in it, said Salt Lake City Fire Department spokesman Scott Freitag.

"As soon as he saw it he put it down," Freitag said.

LDS security was summoned and put the envelopes and powder into a plastic bag. Security officers called 911 and the Salt Lake City Fire Department's Hazardous Material crew and FBI agents arrived.

The man who opened the envelope and two other employees were kept in the annex for more than an hour. Their clothes were washed on site. Only the man who opened the envelope got a small amount of powder on his hand, Freitag said. It was determined the employees were not injured and later went home.

HAZMAT crews used a bleach-like product to sanitize the annex just to be safe, Freitag said. The annex office is in a separate building near the temple. Temple Square was not evacuated while HAZMAT crews were there.

Freitag said he didn't know where the envelope was mailed from but that it didn't appear to contain a letter. Investigators are trying to determine who sent it.

Church spokesman Scott Trotter said he was unaware of any threats called into the temple Thursday that would indicate the envelope was coming.

FBI agents in Los Angeles were investigating the discovery of a similar white powder Thursday at an LDS temple there.

The Los Angeles temple has attracted angry protesters since Proposition 8 -- which reverses a state Supreme Court ruling allowing same-sex marriage -- was approved Nov. 4 by California voters. Investigators said they had no evidence yet directly connecting the the envelopes to the demonstrations, the Los Angeles Times reported Friday.

The LDS Temple-area grounds in Salt Lake City also were the recent focus of pro-gay rights demonstrators, since The Church of Jesus Christ of Latter-day Saints played an active part in organizing support and campaign funding for Proposition 8.