A scientist in the United States who is being questioned about last year's series of anthrax attacks has angrily protested his innocence.

I have never worked with anthrax, I know nothing about this matter

Steven Hatfill

Doctor Steven Hatfill, who is an expert on biological weapons, insisted that he was a loyal American who loved his country.

"I have had nothing to do in any way, shape or form with the mailing of these anthrax letters and it is extremely wrong for anyone to contend or suggest that I have," Doctor Hatfill said.

"I have never worked with anthrax, I know nothing about this matter."

Hatfill made a media statement protesting his innocence

Dr Hatfill said he was appalled at last year's "biological terrorism," when a series of anthrax-tainted letters were posted to government and media offices in the weeks following the 11 September terror attacks on New York and Washington.

Five people died and 13 others fell ill from the deadly bacteria.

"But I am just as appalled that my experience, knowledge, dedication and service relative to defending the United States against biological warfare has been turned against me in connection with the search for the anthrax killer," he said.

No one had come up with a shred of evidence against him, he insisted, and he went on to complain of character assassination.

'Person of interest'

Dr Hatfill used to work as a scientist at a US army base outside Washington that researches biological warfare.

The base was once a store for the same strain of anthrax that was used in the attacks.

While the FBI say he is not a suspect, Dr Hatfill's home has been searched twice.

In the most recent search, news organisations seemed to have been alerted.

A news helicopter hovered overhead when FBI and postal service agents went in.

The BBC's Jon Leyne in Washington says that FBI officials have said privately that Dr Hatfill is one of 30 scientists being investigated.

He adds that although the FBI describes Dr Hatfill only as a person of interest, news media seem to have been given the strong impression that he is a prime suspect in the deadly series of attacks.