The charges are a personal matter, Ms Stewart says

"I want you to know that I am innocent - and that I will fight to clear my name," she wrote in a letter published in USA Today and online at Marthatalks.com.

On Wednesday Ms Stewart was charged with securities fraud and obstruction of justice in relation to trading in shares of biotech firm ImClone.

She later resigned as head of her company, Martha Stewart Living Omnimedia, which trades on her reputation as a tasteful homemaker.

"I am confident I will be exonerated of these baseless charges," Ms Stewart wrote.

'I simply returned a call'

In her brief letter, Ms Stewart attempted to shield her company from the effects of any legal action, pointing out that the charges were a purely personal matter.

Ms Stewart sold ImClone shares the day before regulators rejected the company's application to market the cancer drug Erbitux.

The accusation is that she was acting on a tip-off from her friend, ImClone founder Sam Waksal, who has already admitted charges of securities fraud.

"I simply returned a call from my stockbroker," Ms Stewart wrote.

"I later denied any wrongdoing in public statements and in voluntary interviews with prosecutors. The government's attempt to criminalise these actions makes no sense to me.

"I am confident I will be exonerated of these baseless charges."

Dealing difficulties

Ms Stewart's case is still at an uncertain stage.

The charges levelled so far revolve around her alleged attempts to conceal wrongdoing, rather than insider dealing, an offence extremely difficult to prosecute successfully.

She is, however, being sued by the Securities and Exchange Commission (SEC), the US stock market regulator, for insider trading.