Just two weeks before the start of the Democratic National Convention a string of security scares have federal investigators working to downplay potential terrorist threats.

Almost two weeks ago, a jihadist Web site posted a call to poison a major city's water supply. The posting, reportedly discovered Aug. 9 on a site favored by Al Qaeda, called for an attack on "atheist Europe," a reference that some terror watchers believe represents Western nations in general.

Just days later a Canadian immigrant was found dead in a Denver hotel room with a pound of cyanide, only blocks away from the site of the Democratic National Convention.

Both cases have mobilized federal investigators into action, although they say that neither case carries any real terror threat.

One U.S. official confirmed intelligence analysts are reviewing the Web posting, but said it appeared to be a garden-variety threat the intelligence community sees from time to time.

The FBI also said that it continues to investigate the case of 29-year-old Saleman Abdirahman Dirie of Ottawa, but the Dirie case may not lead anywhere. The key witness with all the answers — Dirie himself — is dead after investigators say he ingested a concoction of the chemical and water.

FBI spokeswoman Kathy Wright told FOX News that the bureau knows where Dirie got the cyanide, but she said releasing the details now could hinder their investigation.

Wright said that there is “no information [tying] him to the Democratic convention later this month in Denver or to terrorism.”

At this time, no one is linking the discovery of cyanide in Denver, to the Web posting. But the incidents have sent up red flags, and made some question the bizarre timing of the two.

The U.S. official commenting about the water-supply threat added it appeared to be in the “aspirational” category — in other words, it is an effort to encourage like-minded followers to execute their own operations in the name of Al Qaeda.

Last month government officials quietly stepped up counterterror efforts because of their growing concern that Al Qaeda or similar groups might try to capitalize on high-profile events like the Olympics and the upcoming conventions.

For a would-be terrorist planning a strike, the Web threat provided tips on how to carry out an attack, counseling operating in small groups to avoid detention. According to one security expert, some jihadists favor smaller, less-elaborate attacks that have a greater chance of success, particularly those targeting a country's economy.

The post offers other advice, telling planners not to use their cars near the target site or their cell phones during the execution of operations and, of course, to leave the country immediately after the operation is done.

The official said that the call to poison a city's water supply is the type of threat that can spread fear and panic, but stressed that it is not feasible.

It's unclear whether the response to the two incidents have anything to do with the Department of Homeland Security's declared period of heightened alert. But experts say this is a time frame when terrorists may have more incentive to attack.

Catherine Herridge is an award-winning Chief Intelligence correspondent for FOX News Channel (FNC) based in Washington, D.C. She covers intelligence, the Justice Department and the Department of Homeland Security. Herridge joined FNC in 1996 as a London-based correspondent.