A letter purported to come from Al Qaeda denied responsibility for bombings that killed at least 117 people during a Shiite Muslim festival in Iraq, blaming American troops instead — but it also called Shiites "infidels."

"The American troops have carried out a massacre to kill innocent Shiites in Karbala (search), their [Shiites'] infidel city, and in Baghdad," said the letter, received on Wednesday via e-mail by the London-based Al-Quds Al-Arabi newspaper and shared with The Associated Press in Cairo.

"We say to the Muslims that we are innocent of this act, and that we are not guilty of worshipping as Shiites worship, except that we believe in God."

Al Qaeda, led by Usama bin Laden, is a predominantly Sunni militant group, and draws its members from some of the most conservative streams of Sunni thought — segments of Muslim society that consider Shiites heretics.

The letter was signed by Al Qaeda's Abu Hafs al-Masri Brigades (search), and its authenticity could not be verified. Al Qaeda often claims responsibility for suicide bombings, but it is unusual for it to put out a message indicating it was not involved in a certain attack.

Last year, it reportedly issued a statement to the Al-Arabiya television network denying responsibility for an Aug. 29 bombing in Najaf, Iraq that killed Shiite leader Ayatollah Mohammed Baqir al-Hakim (search).

Lately, its claims have come in the form of audio or video tapes made available on Islamic Web sites or sent to Arabic satellite television stations.

An editor at the newspaper said that the letter was received via e-mail Wednesday, a day after the date written on it, and that the paper intended to publish it in its Thursday edition. The newspaper's chief editor was not immediately available to comment on the letter.

The letter spelled out that Al Qaeda has clear objectives: "We strike at American Crusaders, their allies and the Iraqi police, stooges of the Americans and the instrument America uses to strike the holy warriors in Iraq. We strike American stooges in the infidel [Iraqi] governing council and those who work with them, whether Sunnis or Shiites."

Iraqi clerics and politicians, Shiite and Sunni alike, have characterized the attacks as Al Qaeda attempts at sparking a sectarian war.

American forces have intelligence connecting the bombings to Jordanian Abu Musab al-Zarqawi (search), a militant also linked to Al Qaeda, the U.S. military commander in the Middle East said Wednesday.

"The level of organization and the desire to cause casualties among innocent worshippers is a clear hallmark of the Zarqawi network and we have intelligence that ties Zarqawi to this attack," Gen. John Abizaid, head of the U.S. Central Command, told a Congressional committee.

An alleged letter by al-Zarqawi, intercepted by the United States in January, proposed attacking Shiite religious sites to draw them into a civil war against Sunni Arabs.

Iranian vice president Mohammad Ali Abtahi also has blamed Al Qaeda for the attacks, saying in a message posted on his personal Web site that the group considers Shiites their "ideological enemy."

U.S. Brig. Gen. Mark Kimmitt, deputy chief of operations in Iraq, on Wednesday dismissed Al Qaeda's purported denial, though he did not comment on the letter's authenticity.

"I saw that statement that said Al Qaeda did not do it, and if you read further in that statement you find that it directly blames the Americans," Kimmitt said.

"If the first part of the statement is as ludicrous as the second part of the statement. I think it stands on its own," he said.

The purported Al Qaeda letter made clear its authors considered Shiites heretics. It referred to being innocent of sharing Shiite beliefs and called largely Shiite Karbala an "infidel city."

It said it doesn't kill innocent people "except in carrying out justice" against those who don't share its beliefs, in what was a clear reference to Shiite Muslims.

Tuesday's bombings came as Shiites mourned the death of Imam Hussein (search), the grandson of Islam's founding Prophet Muhammad. The death of Hussein and his 72 companions in A.D. 680 on the plains of Karbala, in modern Iraq, was part of a leadership dispute that arose after Muhammad's death. It caused the split in Islam between Shiites and the majority Sunni Muslims.