(CNN) Dozens of businesses and institutions across the United States and Canada received email threats Thursday afternoon, prompting evacuations and sweeps of buildings.

Guy Dickinson tweeted this photo of police at 17th Street and K Street Northwest in Washington, DC on Thursday afternoon.

At this time it's unclear if the threats -- which have been received in San Francisco, New York, Seattle, Miami, Washington, DC and other locations nationwide -- are connected. The FBI and the Bureau of Alcohol, Tobacco, Firearms and Explosives said they are aware of the threats and are working with law enforcement to provide assistance.

"As always, we encourage the public to remain vigilant and to promptly report suspicious activities which could represent a threat to public safety," the FBI said.

Email threats also have been received in Vancouver, Ottawa and Toronto, Canada.

Vancouver Police Department Sgt. Jason Robillard tells CNN that businesses have received threats. He is not aware of any buildings that have evacuated.

Read More