A rash of bomb threats was emailed on Thursday to hundreds of businesses, public offices and schools across the United States and Canada demanding payment in cryptocurrency, but none of the threats appeared credible, law enforcement officials said.

Initial jitters sparked by the wave of awkwardly worded messages, threatening to set off explosives unless $20,000 were delivered in bitcoin, subsided within hours as some local authorities began referring to the electronic extortion notes as a scam.

One email targeting a St. Louis-area middle school was traced by local investigators to an internet protocol, or IP, address in Moscow, the sheriff’s office in Lincoln County, Missouri said.

The officials cautioned that such an IP address does not prove it came from Russia because the sender could have electronically laid a false trail to cover up its true origin. They suggested instead that the flurry of emails were part of a wide-scale digital hoax.

Six hours into the security scare, no actual explosives had been found, authorities said. But the threats prompted brief evacuations of a Toronto subway station and a newspaper office in Raleigh, North Carolina. Some public schools and businesses also were evacuated as a precaution.

Among other cities where bomb threats were reported by authorities were Washington, New York, Detroit, San Francisco, Los Angeles, Phoenix, Oklahoma City, Grand Rapids, Iowa, Denver, Ottawa, and Calgary, Alberta.

Several hours after North America was hit, similar email threats were showing up in New Zealand, according to police there.