A U.S. source reportedly sent more than 400 bomb threats to dozens of schools across the United Kingdom, causing some to be evacuated, law enforcement announced Monday.

The threats, sent via email to 35 schools, warned of a pre-placed explosive device to be detonated if the school failed to provide a $5,000 cash payment, U.K. police said, The Guardian reported Monday. Law enforcement received reports of the threats, examined the emails, and eventually concluded there was no credible menace. Authorities advised schools to not close upon receiving one.

“We have received reports from a large number of schools in our region that they have received threatening emails. The emails inform the school that a bomb has been placed on the grounds and will be detonated if they don’t hand over cash,” a police spokesman told The Guardian. “Detectives have looked into the emails — which appear to originate from the US — and can confirm that there is no visible threat. We take all incidents of this nature extremely seriously, and an investigation into the emails in question is under way.”

Several schools in London closed in response to “malicious communications” but re-opened hours later following the police report. It is unclear whether the U.K. will seek an investigation into the alleged U.S. source of the threats. No arrests have been made in the U.K.

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Pictures of the reported email have surfaced on social media.

“This is a message to EVERYONE. We have sent in a student with a bomb,” the email reportedly read. “The bomb is set to go off in 3 hours time. If you do not send $5,000 USD to payments@veltpvp.com. If you do not send the money! We will blow up the device. Our site has all the information needed (veltpvp.com). If you try to call the cops, we will blow up the device on the SPOT! ANY attempt at defusing it your self will cause it to explode.”

The website, VeltPvP.com, is a player community for the video-game Minecraft. They denied any involvement in a statement on Twitter.

We have nothing to do with the bomb threats that were sent out to the 400+ UK schools. We’ve been being harassed by a group of cyber criminals that are trying to harass us in anyway possible. We’re extremely sorry for anyone who had to deal with this, but just know it’s fake. — VeltPvP (@VeltPvP) March 19, 2018

“We have nothing to do with the bomb threats that were sent out to the 400+ UK schools,” the site stated. “We’ve been being harassed by a group of cybercriminals [who] are trying to harass us in anyway possible. We’re extremely sorry for anyone who had to deal with this, but just know it’s fake.”

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