Canadian police and intelligence agencies will announce multiple arrests on Monday after an operation to thwart a "major terrorist attack," the Canadian Broadcasting Corporation reported, citing unidentified "highly placed" sources.
The Royal Canadian Mounted Police said in a statement that they would provide details about a "national security criminal investigation" at a news conference at 3:30 p.m. ET (1930 GMT)
The statement, which gave no details of arrests, said security forces had conducted joint operations in Toronto and in Montreal, Canada's two biggest cities.
U.S. officials said the alleged plot was not linked with last week's Boston Marathon bombings. CBC said the operations was conducted with the U.S. Department of Homeland Security and the FBI.
The arrests follow not only the Boston bombings but revelations that Canadians took part in an attack by militants on a gas plant in Algeria in January.
It also recalls the arrests in 2006 of a group of more than a dozen Toronto-area men accused of planning to plant bombs at various Canadian targets.