WASHINGTON: A rash of bomb threats were 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.

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.

But US government sources speaking on background to Reuters said that such findings were inconclusive and that federal investigators doubted that Russians or the Russian government were involved.

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 widescale digital hoax.

The security scare began shortly before 2 PM EST (1900 GMT) as police departments in major US cities coast to coast began reporting on Twitter that numerous local businesses had received the menacing emails — awkwardly worded threats to set off a bomb unless a bitcoin payment of $20,000 was received.

Four 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.

Lincoln County, Missouri, sheriff’s spokesperson Lieutenant Andy Binder said authorities bused the students from a middle school receiving one of the threats to another campus as a precaution, but the school was later determined to be safe and classes will resume there on Friday.

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