This story was in today's New York Times:

Iran Aiding Shiite Attacks Inside Iraq, General Says

Iran has stepped up its support for violent Shiite groups in Iraq and is providing the weapons and training so they can attack American troops, the top American commander in Iraq said Thursday.

"They are using surrogates to conduct terrorist operations in Iraq both against us and against the Iraqi people," the commander, Gen. George W. Casey Jr., told reporters. "It is decidedly unhelpful." He said that the Iranian assistance had increased since January and that this had emerged as an important factor in weighing further reductions in American forces in Iraq....

"We are quite confident that the Iranians, through their covert special operations forces, are providing weapons, I.E.D. technology and training to Shia extremist groups in Iraq," the general said....

Here's what I find strange about this: only a week ago, we were being told we should believe in the genuineness of a letter found in Abu Musab al-Zarqawi's safe house, which suggested that Zarqawi was deceiving us about Iranian ties to the insurgency:

The question remains, how to draw the Americans into fighting a war against Iran? ... it is necessary first to exaggerate the Iranian danger and to convince America and the west in general, of the real danger coming from Iran, and this would be done by the following:

1. By disseminating threatening messages against American interests and the American people and attribute them to a Shi'a Iranian side.

2. By executing operations of kidnapping hostages and implicating the Shi'a Iranian side.

3. By advertising that Iran has chemical and nuclear weapons and is threatening the west with these weapons....

5. By declaring the existence of a relationship between Iran and terrorist groups (as termed by the Americans)....

I had my doubts about the authenticity of that letter, as I said when it was released. (I like what one of my commenters said: "We need to start making body armor from terrorists' papers and passports. Those things are indestructible.") But it was widely assumed to be genuine. (It was very comforting to think so, because the main thrust of the letter was that Zaqawi was saying, "We suck as terrorists.")

So, which is it? Are the Iranians involved in the Iraqi insurgency? Or is the Zarqawi letter legit?