Threats have been made against the CIA operative whose unmasking is at the heart of the political scandal rocking President George W Bush's presidency, her husband said yesterday.

Joseph Wilson, a former American diplomat, said there had been "specific threats " against his wife Valerie Plame and that the couple had talked with "several agencies" about extra security to protect her.

In a television interview to be broadcast tonight, Mr Wilson would not discuss who might be behind the threats. Ms Plame's cover was blown two years ago after her husband wrote accusing Mr Bush of misleading the world over the reasons for going to war in Iraq.

An investigation into the leaking of Ms Plame's identity to the media has led to the indictment of Vice-President Dick Cheney's chief of staff, Lewis "Scooter" Libby, on five charges of perjury and obstruction of justice.

Mr Libby, who resigned on Friday, faces up to 30 years in prison and a fine of $1.25 million (£700,000) after the special prosecutor, Patrick Fitzgerald, accused him of lying to FBI agents when he claimed that he had learnt of Ms Plame's true identity only from reporters.

It is a criminal offence to disclose the name of undercover intelligence officers. No one has yet been charged with revealing Ms Plame's identity, although Karl Rove, Mr Bush's senior political adviser, remains under investigation.

Senior officials at the CIA's headquarters in Langley, Virginia, are reported to be still assessing the damage done to its operations, including the possibility that the lives of other agents who used similar "cover" may have been put at risk.

Mr Wilson said his wife "felt like she'd been hit in the stomach" when she saw her name in newspapers. She immediately began "making lists of what she had to do to ensure that her assets, her projects, her programmes and her operations were protected".

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