Law enforcement agencies across the US and in Canada responded Thursday to a wave of bomb threats against schools, businesses, government buildings and other institutions, according to the FBI and news reports.

The threats, many received by email, have promoted evacuations, lockdowns, panic and disruption, according to various reports. But several police agencies said the threats lacked credibility.

"We are aware of the recent bomb threats made in cities around the country, and we remain in touch with our law enforcement partners to provide assistance," the FBI field office in Washington, DC, said in a statement. "As always, we encourage the public to remain vigilant and to promptly report suspicious activities which could represent a threat to public safety."

The New York Police Department said that an email being circulated contained a bomb threat and asked for payment in Bitcoin, matching similar reports from police agencies elsewhere.

"At this time, it appears that these threats are meant to cause disruption and/or obtain money," the department said in a statement on Twitter. "We'll respond to each call regarding these emails to conduct a search but we wanted to share this information so the credibility of these threats can be assessed as likely NOT CREDIBLE."

According to a statement published on Facebook by the police in Cedar Rapids, Iowa, several businesses in that city received the same emailed threat.

In it, the sender claimed that an explosive device had been hidden "in the building where your business is conducted" and could be prevented from detonating with a $20,000 ransom payment, made using Bitcoin, a cryptocurrency.

"I can call off my man if you make a transfer," the sender wrote.

The Massachusetts State Police said that it was working with federal and local officials to assess the risk associated with threats to businesses there.

The San Francisco Police Department said it had begun responding to reports of bomb threats at about 10 am.

Similar threats were received throughout the country, from Washington state to Colorado to Georgia, and even in Canada, according to various reports. The targeted institutions also included libraries, banks and medical facilities.