© Bruce Aalhus/Global News Calgary police responded to Centennial High School as well as many others amid a rash of swatting calls on Monday, Feb. 11, 2019.

Three teenagers have been charged in a massive international school "swatting" incident in February. Charges are pending against another in England as well, Edmonton police announced Thursday.

On Feb. 11, multiple schools in Edmonton began receiving phone calls threatening either a bomb or impending attack by an armed suspect. The schools were placed on heightened alert, and in some cases initiated lockdown procedures, while members of the Edmonton Police Service responded.

Officers were told the calls were made using an online app and that the caller had either an English or Scottish accent. The EPS School Resource Officer Unit began coordinating with affected schools and it became clear they were part of a large-scale hoax, according to police.

The EPS Cyber Crime Unit was able to link the calls to similar ones being made to Calgary schools and even a school in Texas.

READ MORE: 4 Calgary schools locked down as police respond to swatting calls

In total, nine schools and one bank in Edmonton were called with the threats and five schools in Calgary received similar calls over the course of Feb. 11, 12 and 20.

After an investigation, police said the calls were traced back to the United Kingdom. After contacting officers in the UK, EPS officers learned the calls were linked to over 80 similar hoax calls made to the Netherlands, England, Scotland and the USA.

Police from Canada, the U.S., the Netherlands and the UK collaborated on the investigation and laid numerous charges against three youths. The teens cannot be named, but police said they are between 15 and 17 years old.

“The amount of school and police resources these calls take up, not to mention the distress they cause to children, teachers and parents, is unacceptable,” Det. Philip Hawkins, with the EPS said.

“We left no stone unturned in this lengthy investigation, even across international borders, and three suspects are now facing charges in their home country."

Each teen is facing six charges under Scottish law that include charges under criminal law, the communications act, the postal services act and wasting police time, the EPS said.

In total, the series of calls resulted in 47 EPS vehicles being deployed and affected more than 4,000 Edmonton students. Six schools were placed in lockdown for a total of 4.75 hours.