The US is on high alert this weekend amid fears of an outbreak of biological terrorism, fuelled by the confirmation of a fourth case of anthrax exposure.
President Bush said the new confirmed case "has got to cause concern." He said "our nation is still in danger," echoing warnings on Thursday from the FBI that further terrorist attacks may be planned over the coming days.
Health authorities reported the identification of a fourth case of anthrax exposure in the office of the NBC television network in New York City.
Two further possible cases were being investigated. Yesterday afternoon the offices of the New York Times were closed, following the opening of a letter containing an unknown white powder. A similar alert took place in Washington at the State Department. Later, the New York Police Department said tests on the substance in the New York Times had proved negative.
While there is no indication of who was responsible for the anthrax outbreaks in Florida and New York, they have further increased the nervousness of a nation already fearing retaliation from Osama bin Laden's network for the military strikes on Afghanistan.
The US Vice President, Mr Dick Cheney, said yesterday there could be links between the discovery of four anthrax cases in the United States and Osama bin Laden.
Mr Cheney said although there was not enough evidence to positively pin down a connection, the cases of anthrax in Florida and New York were "suspicious".
"I think the only responsible thing for us to do is proceed on the basis that it could be linked," Mr Cheney told journalist Jim Lehrer in an interview on PBS's News-Hour.
Mr Cheney said the United States had ample evidence that bin Laden's followers had been trained in how to spread biological and chemical weapons.
The second deliberate infection of a media company fuelled fears of a political dimension to the attacks. Reports suggests that at NBC the well-known newscaster Tom Brokaw was the addressee on the letter believed to have caused the infection, while the alert in the New York Times was caused by a letter addressed to bioterrorism expert Ms Judith Miller.
Last night, however, an FBA official, Mr Barry Mawn, said the envelopes sent to NBC and the New York Times both came from the town of St Petersburg in Florida. He said the envelopes were "business-type letters from an anonymous individual ... postmarked from St Petersburg in Florida.
The US and Britain yesterday eased their attacks on Afghanistan, in deference to a Muslim holy day. As reports said the anti-Taliban United Front (Northern Alliance) had won new territory in central Afghanistan, the US Secretary of Defence, Mr Donald Rumsfeld, urged opposition groups inside the country to move against the Taliban in areas where the US has bombed.
"We feel we have done a certain amount with respect to those Taliban and al-Qaeda military targets and it may very well be more appropriate for ground forces to be moving in areas where we previously have been bombing," Mr Rumsfeld told reporters. He appeared to be referring to the United Front fighters, who have been advancing towards Kabul.
"Military operations continue," said Gen Richard B. Myers, chairman of the Joint Chiefs of Staff. "But we are not doing any pre-planned operations today, as Friday is the Muslim holy day."
The UN Human Rights Commissioner, Mrs Mary Robinson, called for a suspension of the strikes to provide aid to hungry civilians before the onset of winter.
