WASHINGTON, 30 October — The White House Sunday rejected reports that the anthrax sent to the Senate contained bentonite, an additive used in Iraq’s biological weapons program.

"Based on the test results we have, no bentonite has been found," White House spokesman Scott Stanzel told journalists. "As always, there will be continuing tests."

Stanzel was responding to reports by ABC News and other news sources that bentonite had been detected in the anthrax that was mailed to the office of Senate Majority Leader Tom Daschle, D-South Dakota.

Ari Fleischer, White House press secretary, later told ABC that the tests had found no bentonite, which is used to prevent anthrax particles from sticking together, which allows them to become airborne.

Fleischer also said the tests detected no aluminum, which would normally be present in bentonite-enhanced anthrax. Bentonite had been used in Iraq’s biological weapons program, but it had also been used elsewhere, including the United States.

Dr. David Franz, former commander of the US Army’s Research Institute of Infectious Diseases told ABC’s ‘This Week’: "Bentonite is available from chemical companies, a number of them are in the United States and throughout the world."

He cautioned that even if investigators link the anthrax to a particular region of the world — it would not eliminate the possibility that the anthrax was moved before being mailed to Sen. Daschle.

"It’s not like the bullet and rifling relationship in ballistic forensics," Franz explained. "It’s not like when you have a bullet with the marks on it from specific barrel, you’ve got a definite answer. That’s not the way biology works."

"Even if we have definitive proof that we have bentonite in a sample from the Daschle letter, in my mind, that’s just another piece of the puzzle. It’s not the final piece of the puzzle," the former infectious disease expert said.

White House spokesman Fleischer said last Friday that tests on the anthrax sent to Sen. Daschle proved that even someone with a Ph.D. in microbiology could have produced the poison in a small laboratory. This news broadened the list of possible masterminds of the anthrax attacks to people or groups not linked to foreign governments.

Federal law enforcement and intelligence sources, meanwhile, are warning that terrorists groups could be using anthrax attacks as a diversion to take advantage of an overburdened law-enforcement system to plan more attacks on America.

FBI Director Robert Mueller told a group of the country’s mayors over the weekend that more than 7,000 of its 11,000 agents and support personnel are working on investigations relating to the Sept. 11 and anthrax attacks. "And we still have to deal with the hoaxes," he said.

Journalists, however, appear to be losing their patience with the Bush administration over the anthrax scare. Health and Human Services Tommy Thompson and Homeland Security Chief Tom Ridge are taking the brunt of the criticism.

The Los Angeles Times says there are "concerns that Thompson, the government’s top health official is out of his depth. And Tom Ridge "has at moments, critics say, seemed misinformed," reports NBC’s Campbell Brown.

But the American public does not appear to agree with the media’s criticisms. An ABC News polls found that 92 percent of Americans think their own mail is safe. In a USA Today survey, 77 percent said they are confident the government can respond effectively to a major outbreak of anthrax. And 60 percent said the media are overreacting to the anthrax threat.