UNITED NATIONS (CNN) -- A "high probability" exists that al Qaeda will attempt an attack using a biological, chemical, radiological or nuclear weapon within the next two years, according to a U.S. report presented to a U.N. committee. The report -- submitted April 17 -- predicted that al Qaeda "will remain for the foreseeable future the most immediate and serious terrorism threat facing the United States."

The image at right, from a CNN new source, comes from a captured video tape of a chemical weapons experiment on a dog. The U.S. and other advanced "powers" ran tests such as these many years ago, but have since stopped such inhumane testing.

A U.S. diplomat cautioned, however, that "too much is being made" of the two-year time frame. The State Department official who wrote the report -- which was based on existing intelligence -- "judged for himself that the threats appear to cover about two years," the diplomat told CNN. "It was just a choice of words by an individual."

The diplomat said the report did not mean to suggest the United States had specific intelligence about such an incident being attempted within two years. Nor did it mean the threat would end in two years, the diplomat said.

The report did not specify where a strike could occur, but said the terrorist group would continue to "favor spectacular attacks but also may seek softer targets of opportunity, such as banks, shopping malls, supermarkets, and places of recreation and entertainment."

The report said al Qaeda gets "varying degrees of support" from many international terrorist groups. "U.S. government investigations have revealed a widespread militant Islamic presence in the United States," the report said. "We strongly suspect that several hundred of these extremists are linked to al Qaeda."

It added that U.S. investigations have found no evidence that those groups or individuals supporting al Qaeda are "actively engaged in planning or carrying out a terrorist attack."

But it warned that "the support structure is sufficiently well-developed that one or more groups or individuals could be used by al Qaeda to carry out operations in the United States or could decide to act independently."

All U.N. member nations have been asked to submit such reports to the U.N. committee -- established to monitor sanctions on al Qaeda and leader Osama bin Laden, Afghanistan's former Taliban regime and associates of the two groups. The sanctions seek to freeze assets of the groups and their followers.

A spokesman at the U.S. mission to the United Nations said the report's release was delayed because it had to be translated into the agency's six official languages.

CIA Director George Tenet told Congress in February that the United States had intelligence suggesting plots to attack targets in the United States or on the Arabian Peninsula with "the use of a radiological dispersion device as well as poisons and chemicals." That intelligence referred to plots timed to occur at the end of the Hajj, the Muslim pilgrimage that ended in February. Nothing came of the information, though it was part of the reason the U.S. terror threat level index was raised in early February.