The Mormon temple in Westwood was closed Thursday afternoon after an envelope filled with an unidentified white, powdery substance was delivered to temple employees, Los Angeles police said.
About 3:30 p.m., a hazardous-materials team was sent to the temple at Santa Monica Boulevard and Overland Avenue, said LAPD Officer Karen Smith.
The temple has recently been the site of protests by opponents of Proposition 8, though it is unclear whether the envelope was related to protests over the gay marriage ban, officials said.
"It is unknown who it's from or who it's addressed to, or any of that," Smith said.
Laura Eimiller, a spokeswoman for the FBI's Los Angeles office, said agents were investigating.
A similar letter was received at the Salt Lake City Mormon temple about 3:30 p.m. local time today, said Juan Becerra, a spokesman for the FBI's Salt Lake City office.
"Our hazmat team as well as Salt Lake City Fire Department responded, collected the evidence, and it is now at the lab," he said.
The L.A. Gay & Lesbian Center in Los Angeles issued a statement late Thursday decrying the incident.
"While the L.A. Gay & Lesbian Center organized a peaceful demonstration against the involvement of the leadership of the Mormon Church in the deceitful Yes on Prop. 8 campaign, we decry the use or threat of violence. Just as the lesbian, gay, bisexual and transgender community seeks the right to be treated equally under the law, all Americans should have the right to live lives free from fear and violence," the statement said.
Meanwhile, a gay rights activist submitted a formal complaint to the enforcement division of the California Fair Political Practices Commission alleging that the Mormon church failed to report the value of the work, including phone banks, commercials and other services, done to support the Proposition 8 campaign.
Proposition 8, which amends the state Constitution, was approved by voters last week.