BERLIN — Security experts in Germany are investigating whether hijack suspect Mohammed Atta carried anthrax spores allegedly obtained from Iraqi agents to the United States, a German newspaper reported on Thursday.

Germany's Bild daily cited unnamed Israeli intelligence sources as saying Atta, who is suspected of flying a plane that crashed into the World Trade Center, received anthrax spores from Iraqi agents during two visits to the Czech Republic.

The mass circulation newspaper cited investigators as saying they suspected Atta, who had lived in Hamburg, carried the spores to New York where customs officials apparently checked his luggage for drugs but not bacteria.

The anthrax spores that contaminated the air in a Senate office last week had been treated with a chemical additive so sophisticated that only Iraq, the former Soviet Union and the United States are thought to have been capable of making it, the Washington Post reported Thursday.

The Post, quoting sources and experts close to the investigation, said those three nations were the only countries known to have developed the kind of additives that allow anthrax spores to remain suspended in the air and thus become more easily inhaled and more deadly.

But the newspaper said a government official with direct knowledge of the investigation felt that the totality of evidence in hand suggested it was unlikely that the spores were originally produced in the former Soviet Union or Iraq.

Iraqi officials denied this week any link to the release of anthrax bacteria in the United States and accused Washington of fabricating the attacks as a pretext to broaden its anti-terrorism campaign.

Three people have died from inhalation anthrax and nine others have been infected in the United States since letters containing the potentially lethal bacteria were sent through the mail.

Two of the dead were postmen who worked in a Washington facility that processed mail sent to the U.S. Capitol, including a tainted letter that went to the office of Senate Majority Leader Tom Daschle. The other person killed by anthrax was a photo editor at a supermarket tabloid newspaper in Florida.

Meanwhile, the FBI has released the text of three tainted letters sent to Daschle, NBC News and the New York Post. They have virtually identical handwriting and contain the words "Death to America" and "Allah is great."

An entire portion of a Senate office building where anthrax was discovered last week will have to be sealed off indefinitely, Daschle, D-S.D., said Thursday.

He told reporters that anthrax found Wednesday in a new location in that same Hart office building was just a trace amount. Doctors consider the discovery to be relatively low risk and have ordered no new tests of people who may have been exposed to the potentially deadly germs, Daschle said.

Additionally, federal health officials announced Wednesday that a deal had been struck with the Bayer Corp. to buy 100 million tablets of Cipro, the antibiotic use to treat anthrax exposure. Health and Human Services Secretary Tommy Thompson said the government would purchase Cipro for 95 cents a pill — about half the price it usually pays.

Kay Golan, a spokeswoman for the Centers for Disease Control and Prevention, said the number of people the government now has taking Cipro or other antibiotics against anthrax was "approaching 10,000," although she said a precise number was not known.

Health officials pleaded with people not to self-medicate with Cipro purchased over the Internet because the drug can have side effects.

Sen. Bill Frist, R-Tenn., a surgeon, warned Thursday that the nation's food supply may be the next target.

"What bothers me is these terrorists are trying to take down our infrastructure one by one," he said on NBC's "Today" show. "First it was the World Trade Center and airplanes where our transportation system was paralyzed for a while. Second they've been using biological weapons to try to take down our postal system. And if you look ahead, we know that food has been used successfully in the past."

Frist noted only about 1 percent of food imports are inspected and that the roughly 1,000 federal food inspectors are responsible for 53,000 sites. "It is clear that we need to do more in terms of prevention and preparedness," he said.

Meantime, the post office is turning to the latest in anti-bacteria technology to clean the mail, while urging Americans to take the old-fashioned precaution of washing their hands after handling mail since they can't guarantee its safety.

On Wednesday, tractor-trailer loads of mail were being shipped from Washington to a site where electron-beam technology could be used to sanitize them, said Deborah Willhite, a senior postal vice president

The agency was in the process of obtaining similar machines to use in its own facilities as well as state-of-the-art masks and gloves to protect postal workers.

President Bush released $175 million to help the agency, and the postal governing board authorized an additional $200 million in emergency spending to help pay for equipment and other measures.

"We have debated internally since this began whether we could just stand and bald-face say, 'Don't worry, your mail is safe,' " Willhite said Wednesday.

"We're not going to lie to the American people, who have sustained us for 227 years. At this point in time, the mail has a potential risk," she said, adding: "You know, on the risk management scale of life, the mail is pretty low."

Nonetheless, she said people should wash their hands in soap and water after they handle their mail, "just to make sure that if anything is on the envelope, that they're clean."