In a statement, the Royal Canadian Mounted Police said a 23-year-old Illinois woman and 19-year-old local man planned to go to a highly-populated public place on Saturday "with a goal of opening fire to kill citizens, and then themselves."

Authorities have not released details of alleged targets.

At a news conference early Saturday morning local time, RCMP Assistant Commissioner Brian Brennan called the plan a "heinous event," and said it was a close call.

"Had they been able to carry out their intention, the possibility for a large loss of life was definitely there," he said.

Three people have been arrested in connection with the scheme, including two men aged 17 and 20, whose role is unclear.

The American woman was taken into custody at Halifax Stanfield International Airport without incident.

Police found the 19-year-old suspect dead in his rural Timberlea home, near the provincial capital Halifax on Friday. His death is now being investigated by the Serious Incident Response Team.

Police believe they have now captured all persons involved in the plot.

Following a tip-off on Thursday morning of a "potential significant weapons-related threat," authorities say they "acted quickly and intercepted a threat."

Money is also believed to have been seized along with firearms.

Minister for Public Safety Steven Blaney praised authorities' efforts, calling them "a great example of the fine work they do on a daily basis to help keep Canadians safe."

Authorities have called on Canadians to be vigilant, and report anything they think is suspicious.

Canadian Justice Minister Peter Mackay is scheduled to hold a news conference at 8:00 a.m. local time (1300 UTC).

an/kms (dpa, AP, AFP)