AFP/ Halifax

Canadian police said they had foiled a plot that would have seen an armed duo carry out a shooting spree in the city of Halifax on Valentine's Day before killing themselves.

The Royal Canadian Mounted Police in Nova Scotia said a 19-year-old man from the rural town of Timberlea had plotted with a 23-year-old woman from the US city of Geneva, Illinois to open fire somewhere in Halifax on Saturday. Two others were also allegedly involved.

It was not thought to be terror related.

They "had access to firearms and it was their intention to go to a public venue in the Halifax region on February 14th with a goal of opening fire to kill citizens, and then themselves," the RCMP said in a statement.

Police said the Timberlea man was found dead in a home early Friday morning.

The American woman was arrested shortly after -- along with a 20-year-old man -- without incident at the Halifax Stanfield International Airport.

Police arrested a fourth suspect, a 17-year-old boy from nearby Cole Harbour, at a home later on Friday.

"It's a group of individuals that were of the same... mind to commit a heinous event and then take their own lives," RCMP Assistant Commissioner Brian Brennan told a news conference.

Brennan told the press that the plot was not considered to be related to terrorism.

He added that the attack was planned for a venue where a significant loss of life would have been possible, but declined to name an exact location.

The CBC reported that police had warned one venue of the threat.

"We believe we have apprehended all known individuals in this matter and eliminated the threat," the RCMP statement read.

"We are not seeking any further suspects at this time in relation to this investigation."

The RCMP indicated that firearms had been seized as well as money.

- 'We acted quickly' -

Police said they first received word of a "potential significant weapons-related threat" on Thursday morning.

"We became aware, we acted quickly and intercepted a threat," the RCMP said.

The region's Serious Incident Response Team was investigating the death of the Timberlea man.

Timberlea is a small town on the outskirts of Halifax in the rugged and remote Atlantic province of Nova Scotia.

Steven Blaney, the minister for public safety, praised the police operation to thwart the attack.

"These arrests are a great example of the fine work they do on a daily basis to help keep Canadians safe," he said in remarks reported by the CBC.

"We support our law enforcement agencies who work tirelessly to ensure our communities are safe places to live, work and raise families," he said.

All three suspects were being kept in police custody.

Police called on Canadians to be vigilant and report anything suspect to authorities.