A suspicious envelope was mailed to Fremont police over the weekend, possibly the seventh in a string of letters sent to law enforcement around the Bay Area containing a powdery substance, officials said.

About 11 a.m. Monday, an employee recognized an envelope addressed to the police department as looking similar to the letters received by other East Bay law enforcement agencies, police spokeswoman Geneva Bosques said. The envelope was immediately isolated and caused no disruption, police said.

The FBI will analyze the unopened letter, Bosques said.

Four other Alameda County police departments received a scare Friday when envelopes filled with white powder showed up in their mail, prompting FBI involvement and an investigation by hazardous materials crews. San Francisco and Oakland police departments received similar envelopes Saturday.

The substance inside the envelopes at Hayward, San Leandro, Berkeley, San Francisco and Oakland police departments was not hazardous, officials said. San Leandro's envelope contained baking flour, Lt. Greg Lemmon said, but authorities did not identify the substance found at the other stations.

Another envelope delivered to the Union City Police Department was given over to the U.S. Postal Service and FBI for more investigation, police Cmdr. Kelly Musgrave said. Test results weren't immediately available.

At the time, no other police departments reported receiving similar envelopes, but agencies around the Bay Area were alerted to it, Alameda County fire spokeswoman Aisha Knowles said.

No injuries were reported in any of the incidents and the people who handled the envelopes have not shown any signs of illness, authorities said. The police agencies will conduct a joint criminal investigation to find out who mailed the substances to them.

Staff writers Natalia Neysa Alund, Chris De Benedetti and Rick Hurd contributed to this report.