"I don't know if it's authentic," he said. "People who've read it think it is, but I haven't read it."

General Myers, Chairman of the Joint Chiefs of Staff:

He says the question of its legitimacy is still undergoing study. "Authenticity is still being evaluated," he said.

But he says if it is genuine, then it demonstrates al-Qaida links to the ongoing insurgency.

"But the al-Qaida is clearly involved if that letter is authentic," he said.

Asked if defense officials in Washington, by raising questions about the document's authenticity, were backing away from the more confident pronouncements made earlier in Baghdad, General Myers says that is not the case.

"No, I'm just trying to tell you what I know," he said.