"We are still looking for the source. We really have nothing concrete right now," Judy Orihuela, spokeswoman for the FBI's Miami office, told Reuters.

Asked if officials suspected the contamination was a criminal act, she said: "We've got to find the source before we can determine if it's criminal. We just don't know."

Robert Stevens, a photo editor for AMI publication the Sun, died on Friday of a rare form of anthrax. A second man, mailroom employee Ernesto Blanco, has been exposed to the disease but has not contracted it. He is now in a Miami hospital.

Florida health officials said they had still not determined if the anthrax strain was natural or engineered - a fact which could help to decide if the contamination was a criminal act.

Asked at a briefing if they had ruled out a terrorist action, Palm Beach County Health Department Director Jean Malecki said: "We are open to the possibility of anything. We've not dismissed anything."

The cases of anthrax - a very rare disease that experts say can be used as a biological warfare agent - has caused anxiety among a public still nervous over the Sept. 11 attacks allegedly masterminded by Muslim militant Osama bin Laden.

More than 5,500 people were killed in the attacks in which hijacked planes rammed into the Pentagon in Washington and the World Trade Center in New York.

CALLS ABOUT SUSPICIOUS PACKAGES

Amid fears of possible anthrax contamination, authorities also took precautionary measures isolating and treating people in Washington, Virginia and Kentucky. And with Floridians on edge, police and fire officials responded to a spate of calls from residents concerned about suspicious packages.

Palm Beach County tested about 850 AMI employees and others who had worked in or visited the building, as well as their relatives, over Monday and Tuesday.

Florida State Epidermist Steve Wiersma said the tests would be processed by the Centers for Disease Control and Prevention in Atlanta. Nasal swabs could take several days and blood tests longer but so far there had been no new cases, he said.

The CDC said 15 of its specialists were in Florida to investigate the transmission route of the cases. The bacterial disease is spread by spores and generally confined to sheep, cattle, horses, goats and pigs. It is not contagious.

There was a new scare at the Palm Beach Health Department while people awaited tests. Police cordoned it off and took away dust found in an envelope in a garbage bin. It was believed to be construction dust but would be checked by hazardous material experts, police said.

In nearby Deerfield Beach, local fire chief Jim Mathie said his department received calls about suspicious packages in three separate incidents that turned out to be harmless.

"People are being overly cautious," Mathie said. "I'm sure it has a lot to do with the anthrax."

In Naples, on Florida's southwest coast, police closed two buildings housing the offices of a bank and a law firm after staff reported finding a white powdery substance in mail bins. About 80 people were evacuated and underwent a decontamination process, Naples police spokesman Victor Morales said.

FBI agents took samples of the substance away for testing.

SUBWAY SCARE

In Washington, a Metro subway station was closed and 21 people were held in isolation after a fare dodger fired a gun and dropped a plastic bottle containing liquid. A Justice Department official said the incident involved a container of carpet cleaner and did not appear to be related to terrorism.