Many attacks in Iraq have led to more human injury than the suicide bombing inside Iraq's parliament earlier this week. But few have produced the distinct horror that no area in Iraq –not even the highly protected International "Green" Zone –is safe from attack.

The Islamic State of Iraq, an umbrella organization of Islamist groups that is likely to include Al Qaeda in Iraq,declared responsibility.

Militant Sunni Insurgents Don't Like 'Extremism' of Al Qaeda

Among those who expressed dismay at the attack were Sunni insurgent groups, whose primary stated aim is to eliminate the American presence from Iraq. Nine of these groups held a meeting this week to coordinate their efforts against the Islamic State/ Al Qaeda. According to IraqSlogger, the meeting's coordinator stated the groups' opposition: "We categorically reject the style and method of the Islamic State of Iraq … just as we oppose the current Iraqi government, because it is a product of the occupation."

Indeed, some insurgent groups blame Al Qaeda for the occupation. As reported in the Washington Post,

Khalid Awad, a commander of the Jamiat Brigades, another insurgent group in Anbar, said: "We must confess that if it was not for al-Qaeda, neither Iraq nor Afghanistan would have been occupied. For al-Qaeda has awakened the American ogre against the Islamic nation after the September 11th events, and it is still causing disasters."

The Islamic State of Iraq has responded to the emerging split with threats. Al Hayat (Arabic)) reported Al Qaeda's threats this week to "cut off the heads" of opponents. According to the newspaper, Abu Suleiman Utaybi, the legislative head of the Islamic State of Iraq warned Iraqi insurgent groups that, "we'll cut off their hands and beat their necks" if they oppose the ISI.

Odd Bedfellows: Iraqi Insurgents and the Americans?

The hostility between Sunni insurgents and Al Qaeda linked groups focused on regional expansion may lead to an oddly cozy relationship between the Americans and the (anti-American) insurgents. Tribal leaders in Western Iraq have already made the decision that the Americans are a better bet than Al Qaeda, and nationalist insurgents may follow suit. Ibrahim Al Shammari, the spokesman for the Islamic Army, another insurgent group, confirmed this week that Al Qaeda has been killing members of other groups. He also indicated, according to Al Hayat, that the group would welcome negotiations with the United States, mediated by Russia or Turkey, or the EU. The Islamic Army is alleged to have ties to the Muslim Brotherhood.