Antisemitic letters calling for death to Jews have been sent to at least eight synagogues in Canada.
Communities in Toronto, Montreal, Edmonton and Hamilton were among those targeted by an anonymous sender, who is now being investigated by police.
The incidents, which are being treated as hate crimes, were brought to public attention by the Canadian branch of Jewish service organisation B’nai Brith.
One of the letters carried the words “Jewry must perish”, made to appear blood-soaked, around a Swastika embedded in a yellow Star of David.
B’nai Brith said the letter was sent to two synagogues in Montreal, Beth Ora and Shaare Zedek, and a further four synagogues in Toronto.
“At this holy time for Jews and Christians alike, we are reminded that we are members of one community, striving for the preservation of truth and freedom,” Shaare Zedek rabbi Alan W Bright said.
“Vile acts of this nature should never divide us. Rather, they should serve to remind us that we be steadfast in our convictions, consistent in our commitment and courageous in our endeavors to make Canada and the world a better place in which to live.”
Michael Mostyn, chief executive officer of B’nai Brith Canada, said: “Sadly, we’ve seen the swastika make something of a comeback this year, defacing the walls of high schools, university campuses, and public property.
“Today, it is more imperative than ever that we condemn this symbol of racism and hatred.”
According to B’nai Brith, 1,728 antisemitic incidents were reported in Canada in 2016 – a 26 per cent increase on the previous year and the highest figure since records began in 1982.
“Unfortunately, some (people) feel emboldened at this moment in history to express hate toward identifiable groups and Jews in particular,” Mr Mostyn said.
Valérie Plante, the mayor of Montreal, said the threats were being taken very seriously.
“It’s all our responsibility, from politicians to journalists to citizens, to pay attention to rumours, to be vigilant,” she told journalists on Tuesday. “This is not who we are. We are a tolerant and inclusive city.”