White House spokesman Ari Fleischer, who called the woman's death a cause for concern and expressed the president's condolences, said tests at her home in the Bronx and at the Manhattan Eye, Ear and Throat Hospital where she worked have so far proved negative for anthrax.

However, Fleischer said another employee at the hospital had a "suspicious lesion" on her skin and had been tested for the disease. Results of those tests were not yet known.

Since Sept. 11, when hijacked planes were rammed into landmark buildings in New York and Washington killing more than 4,800 people, there have been 16 confirmed cases of anthrax and most of those were identified as coming through the mail.

New Jersey acting Gov. Donald DiFrancesco reported a new case yesterday of suspected skin anthrax in a postal worker employed at a facility near Camden, which would bring the total number infected with anthrax in the United States to 17.

New York City Health Department spokeswoman Sandra Mullin said the Bronx woman, who has been identified as Kathy Nguyen, worked in a storage supply room at the hospital but it was not yet known how she came into contact with anthrax.

"She died early this morning, but I do not have any other details at this point," Mullin said.

Fleischer said FBI investigators had stepped up their investigation into the anthrax cases and were checking to see whether Nguyen had traveled abroad or domestically and who she had come into contact with.

Authorities were also doing an autopsy to learn whether the bacteria that infected the woman was related to those involved in other recent anthrax deaths, he said.

"As a result of that, they will be able to match that up with the other decedents from the previous anthrax cases to see if it is a result from the same type of anthrax or not," Fleischer said.

NO NEW LEADS IN TRACKING SOURCE

Nguyen's death will make it even more difficult for investigators to track down the source of her disease and to trace the last days of her life, which letters she opened, where she visited and whether she noticed anything suspicious.

Neighbors told local television that the woman, who left Vietnam for the United States in the 1970s, lived a quiet life and did not have any family in America.

U.S. Attorney General John Ashcroft told a news conference that investigators were working very hard to find the source of the anthrax but were no closer to cracking the case.

"I'm not in a position to be able to say to you that we are on the brink of making an announcement here. We don't have progress to report at this time," Ashcroft said.

"I can't say that people have any right to think that the risks have abated as it relates either to anthrax or other terrorist risks," he cautioned.

Dr. Anthony Fauci, director of the National Institute of Allergy and Infectious Diseases which is part of the National Institutes of Health, said the New York case was more perplexing than other cases so far.

"All bets are off and we really need to do - the public health officials, the forensic group - have to do a full court press on trying to track this down. This is critical," Fauci told NBC's "Today" show.

Another case in New Jersey, where a female book-keeper has the skin form of the disease, has raised questions about whether she was a victim of "cross-contamination" in which spores from an anthrax-laden envelope contaminated other letters in the postal system.

The woman works in Hamilton township where several postal facilities have been contaminated with anthrax and Fauci said it was "not far-fetched at all" that she received a letter that was cross-contaminated.