The plot thickens. According to this BBC story, al Qaeda says the letter U.S. intelligence says is from Ayman al-Zawahiri to Abu Musab al-Zarqawi is a fake.

The claims by US intelligence are "based on imagination", (says) a statement posted on an Islamist website.

"We in al-Qaeda organisation announce that there is no truth to these claims, which are only based on the imagination of the politicians of the Black [White] House and their slaves," the statement said.

It is not possible to verify either the letter or the subsequent denial.

Here's my earlier posting.