An anonymous letter sent to the RCMP in late 2004 warned of bomb threats to the Montreal Metro system and the U.S. Embassy in Canada by a man affiliated with Osama bin Laden, a secret U.S. diplomatic cable released by WikiLeaks to CBC News reveals.

The letter, dated Nov. 29, 2004, spurred American government facilities across Canada to heighten security. Though the RCMP noted such letters are frequently received and the threat was doubted to be "credible," U.S. Embassy officials said in the document that few such threats specifically mention the U.S. Embassy.

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The Montreal subway was identified as a possible bomb target in 2004, according to a U.S. document released by WikiLeaks. ((Paul Chiasson))

The anonymous letter writer claimed to have overheard a man detailing a possible plot to bomb the Montreal Metro system on Dec. 15 and the U.S. Embassy on Jan. 10.

The brief letter in French, addressed to the RCMP's Montreal headquarters, included the suspected bomb plotter's name and cellphone number.

"According to the drafter, [the man] is affiliated with Usama bin Laden," the diplomatic cable says.

The man was identified by the RCMP as a Tunisian immigrant, 28 years old at the time, who arrived in Canada four years prior and was working as a part-time security officer and car wash attendant. CBC News is not releasing his name since no charges appear to have been laid.

Upon hearing of the possible bomb threat, the U.S. Embassy officials requested an increase in security at government facilities across the country, including in Halifax, Montreal, Toronto, Winnipeg, Calgary, Vancouver, Quebec City and Ottawa.

But U.S. officials appeared frustrated by the four-day lapse between when the RCMP received the anonymous letter and when they alerted the U.S. about the potential threat.

The U.S. officials asked about the delay. "RCMP were unable or unwilling to respond but the indication seemed to be they were proceeding appropriately," the diplomatic cable says.

The RCMP indicated to U.S. officials that they had located the man, planned to arrest him and then give him a polygraph test.

The Tunisian immigrant did not have any known criminal history in Canada, nor did he appear on any watch lists or FBI databases, according to the document.

The RCMP, however, indicated the suspected plotter would be denied a pending Canadian citizenship request. They refused to give a reason to the Americans, citing privacy law limitations.

The U.S. diplomatic cable was part of a batch of Canada-related cables released by whistleblower website WikiLeaks to CBC News and several other media outlets.