The Homeland Security Department in 2010 identified a terrorist plan to contaminate salad bars and buffets at restaurants and hotels with lethal materials, CBS News reported.

The strikes involving ricin and cyanide would have occurred during one weekend at a significant number of establishments. The would-be poisoners are suspected of having connections to the extremist group al-Qaeda in the Arabian Peninsula, which has been tied to a number of plots against the United States.

A handful of security personnel from the hotel and restaurant sectors have received information on the plot from Homeland Security, Agriculture Department and Food and Drug Administration officials, tee report said.

Just 250 milligrams of cyanide could be lethal, an expert told CBS News. "Initially it would look very much like food poisoning," said Susan Ford, a pharmaceutical sciences professor at St. John's University in New York.

DHS declined to comment, saying: "We are not going to comment on reports of specific terrorist planning. However, the counterterrorism and homeland security communities have engaged in extensive efforts for many years to guard against all types of terrorist attacks, including unconventional attacks using chemical, biological, radiological, and nuclear materials," said spokesman Sean Smith. "Indeed, al-Qaeda has publicly stated its intention to try to carry out unconventional attacks for well over a decade, and AQAP propaganda in the past year has made similar reference