|Halifax, Nova Scotia, Canada|
Three suspects were arrested and a fourth was found dead in a suburb of the eastern city.
At least two suspects had intended "to go to a public venue... with a goal of opening fire to kill citizens, and then themselves", police said.
Police officials said the motive did not appear to be terrorism, without providing further details.
Brian Brennan, commanding officer of the Nova Scotia Royal Canadian Mounted Police, said the plot had involved a 19-year-old man from the Halifax suburb of Timberlea and a 23-year-old woman from the US state of Illinois.
The two, he said, had had access to firearms. The Timberlea man was found dead in a house.
A 20-year-old Canadian man was arrested along with the woman at Halifax Stanfield International Airport. The fourth suspect, a 17-year-old Canadian boy, was arrested at a house.
The roles of the latter two suspects has still to be determined by investigators, police said.
"I would classify it as a group of individuals that had some beliefs and were willing to carry out violent acts against citizens but there's nothing in the investigation to classify it as a terrorist attack," said Mr Brennan.
"I can tell you that it's not culturally based."
He added that police believed they had apprehended "all known individuals in this matter and eliminated the threat".
It's not my normal habit of posting a story like this that does not involve terrorism, but the significance of the arrests make it worthwhile. Also, I have pounded Nova Scotia police for the failures in the Rehtaeh Parsons case, so it's only fair to praise them for an excellent piece of work.