(Reuters) — Workers at a Jewish community center and a nearby synagogue in Colorado opened envelopes on Monday containing a white substance and at least one threatening message, police said.

The Boulder Jewish Community Center was evacuated after a letter was found to hold white powder, which was later declared harmless, along with a note that read: “your (sic) have enemies,” police said.

“When deputies arrived on scene they evacuated the building, quarantined the office, the people who were in contact with the envelope, and the envelope itself,” said Commander Heidi Prentup, spokeswoman for the Boulder County Sheriff’s Office.

About three hours later, police said, a similar envelope was opened at the Congregation Har HaShem synagogue, some two miles south of the community center.

Employees there told officers a white substance fell out of an envelope as they were opening mail outside the Reform synagogue, Boulder Police Department spokeswoman Kim Kobel said.

She said the substance was tested and likewise was found to be non-toxic. The building was searched and nothing suspicious was found, she added.