WASHINGTON (CNN) -- Former Deputy Secretary of State Richard Armitage was the source who revealed the identity of CIA officer Valerie Plame to syndicated columnist Robert Novak in 2003, touching off a federal investigation, two sources familiar with Armitage's role tell CNN.

The sources said Armitage revealed Plame's role at the CIA almost inadvertently in a casual conversation with Novak, and it is not clear if he knew her identity was classified at the time.

Armitage was not indicted by the federal grand jury that investigated the disclosure of Plame's name to Novak and other journalists.

In a July 14, 2003, column, Novak noted that Plame was a CIA operative, citing two senior Bush administration officials. The column was primarily about Plame's husband, Joe Wilson, a former career diplomat and critic of the intelligence underlying the invasion of Iraq.

Novak has never revealed the original source of the information about Plame. However, he has confirmed that President Bush's chief political strategist, Karl Rove, confirmed the information and was the second source cited in the column.

Novak has said he would not reveal the identity of the original source unless the source came forward. However, he said the special counsel in the CIA leak investigation, Patrick Fitzgerald, learned who the source was independently.

Fitzgerald has said he does not plan to bring any charges against Novak's original source.