Anthrax case found in New York

Fears of fresh terrorist outrages spread across America on Friday after a woman employed by the NBC television network in New York tested positive for anthrax. It was the fourth reported occurrence this month of a disease that could be used in a terrorist biological warfare attack.

The news, which came the day after the FBI issued a warning about possible terrorist attacks on US targets either at home or abroad this weekend, jangled nerves across the country but nowhere more than on Wall Street, where shares dropped sharply after the news emerged. The price of gold, a traditional refuge in times of uncertainty, jumped $3 an ounce.

America's media establishment was in a state of near-panic. Part of 30 Rockefeller Plaza – where NBC Nightly News, the woman's employer, has its headquarters – was sealed off. The woman is an assistant to the NBC anchorman, Tom Brokaw, according to sources inside the organisation.

In what could be a related incident, Judith Miller, a veteran Middle East correspondent at The New York Times newspaper, received a package containing suspicious powder yesterday. CBS News also closed down its mailroom as a precaution and CNN said it was tightening security.

Law-enforcement officials across the US were on the highest alert on Friday after reporting unspecified but credible threats of retaliation for the bombing campaign in Afghanistan, which began on Sunday. But the FBI said it saw "no connection" between the attacks of 11 September on New York and Washington and the NBC case.

Officials said the origins of the New York anthrax were unknown. But they stressed there appeared to be no link with the cases in Florida, one of which caused the death of Robert Stevens, a 63-year-old British-born picture editor, a week ago.

Two other employees of American Media Inc, which publishes supermarket tabloids and has its headquarters at Boca Raton, Florida, tested positive but are in no danger. The Florida cases are assumed to be of criminal origin but no link has been established with the 11 September hijackers – even though some of the suspects expressed interest in crop-dusting aircraft and had taken flight training nearby.

Mr Stevens died of the rare but most deadly respiratory form of anthrax. The NBC employee has apparently contracted the more common and treatable cutaneous form of the disease, which is often brought about by contact with the tissue or hide of infected animals. Inhalation of anthrax is almost always fatal.

According to officials, the case began with the arrival of a suspicious letter, containing some white powder, at NBC News two weeks ago. After the woman opened it, she reported the incident and was tested for infection. The powder itself was sent for testing but revealed no trace of anthrax.

For many days the woman tested negative but then developed a skin lesion. After re-testing samples at the Centre for Disease Control, a biopsy report came back positive for cutaneous anthrax. She was put on antibiotics and is expected to make a full recovery.

NBC staff were told what had happened over the office intercom and were given the choice of leaving the building. More than half of the employees left, one said. "I don't like the air quality there, I just feel nervous about it," she added.

At a hastily convened news conference, Rudolph Giuliani, the Mayor of New York, said that the move to seal off part of the Rockefeller Plaza building had been done "from an excess of caution". He declared the chances "very good" that the infection had been contained, since any other case would have come to light by now.

Moving to reassure the country, Tommy Thompson, the Health and Human Services Secretary, said there was "no proof whatsoever" that the case of anthrax found at NBC News was terrorism.

This latest case in New York is especially unsettling because of where it happened – not in faraway Florida but in the city which took the brunt of the 11 September attacks and is the heart of the US financial and media industries.

In London, police and anti-terrorist officers have been placed on heightened security alert after reports that Britain was being targeted by Islamic extremists. Sources have told The Independent that there is a "non-site specific" threat aimed at Britain, although no individual targets have been identified. Police have deployed an extra 1,500 officers on the streets of London.