**Veteran US newspaper columnist Robert Novak,78, has died after a battle with brain cancer.**Mr Novak made headlines in 2003 when he revealed the identity of covert CIA agent Valerie Plame in a column.
The leak led to a long-running criminal investigation into senior Bush administration officials.
From 1963 until his retirement in 2008, Mr Novak - a staunch conservative - wrote an influential political column that was syndicated throughout the US.
‘Tireless reporting’
In 2003, he came under fire for a column in which he revealed that “two senior administration officials” had told him that Valerie Plame - the wife of a US ambassador who had voiced doubts about the Bush administration’s case for the war in Iraq - was a CIA operative.
Disclosing the identity of a covert agent is illegal in the US, and as a result of the column a special prosecutor was appointed to look into whether Bush officials had broken the law.
An aide to Vice-President Dick Cheney, Lewis “Scooter” Libby, was eventually convicted of perjury as a consequence of the investigation.
Senate Republican Leader Mitch McConnell paid tribute to Mr Novak, saying he “explained the politics and the personalities of Washington to readers across the country through a mix of tireless shoe leather reporting and the kind of keen insight that can only be gained through years and years of dedication to a craft.”