The practice, called "swatting," has been increasing in both countries in recent months, ABC News reports.
A swatter or group of swatters is often behind multiple incidents, and copycatting is common, said Kevin Kolbye, the assistant special agent in charge of the FBI's Dallas office, which headed the first federal swatting case in 2007.
"Same as you find when a highly publicized serial killer is around, you find a lot of copycatting," Kolbye said. "So when crimes receive national attention, you find people who are intrigued with this type of crime and they emulate it."
Swatters often are males in their 20's and 30's who fake hostage situations for "bragging rights," Kolbye said. They can face federal charges of conspiracy, carrying a maximum penalty of five years in prison, and fraud, with a maximum of 20 years.
In Wyckoff, N.J., 40 members of a Bergen County Police Department SWAT team responded July 23 to a call from a man who said he had killed four people and taken several others hostage. After throwing tear gas through windows, the SWAT team members found only a cat.
Such calls divert officers from legitimate police work and place innocent people in danger, Wyckoff Police Chief Benjamin Fox said.
"You've got police officers running around with high-powered weapons acting under belief of a potential threat against them," he said. "What's if there's an accident? What if somebody innocently comes out of their house because of the hoax and it's perceived by officers on scene as someone else?"