BAGHDAD — An insurgent umbrella group that includes al-Qaida in Iraq claimed Friday one of its "knights" carried out the parliament suicide bombing in Baghdad's Green Zone, and the U.S. military revised the death toll sharply downward to one dead.

The Islamic State of Iraq said in an Internet posting that it had delayed issuing the claim of responsibility to allow its men time to flee.

Iraqi officials, who spoke on condition of anonymity because the investigation was incomplete, said the bomber was believed to have been a bodyguard for a Sunni lawmaker who was not among the casualties. The officials did not name the lawmaker.

"A knight from the state of Islam ... reached the heart of the Green Zone ... the temporary headquarters of the mice of the infidel parliament and blew himself up among a gathering of the infidel masters," the Islamic State said in the statement posted on one Islamist Web site commonly used by insurgents.

The SITE Institute, which tracks militant postings, said the claim appeared authentic. Some media reported on Thursday that al-Qaida in Iraq had issued a claim an hour after the attack, but the Islamic Web forum on which it was reportedly posted was not among those used by the Islamic State in Iraq, so SITE cast doubt on its authenticity.

In a statement Friday morning, the U.S. military said "after further research and consultation with government of Iraq officials" it had determined that only one "civilian" had been killed in the attack and 22 were wounded.

Parliament officials said the victim was Mohammed Awad, a moderate Sunni lawmaker. Seven of the wounded were members of parliament, the officials said.

U.S. military spokesman Maj. Gen. William Caldwell had said Thursday that eight people were killed in the bombing, a major security breach in the most heavily guard region of Baghdad.

Iraqi lawmakers, meanwhile, gathered Friday in a rare — and defiant — session of parliament on the Muslim day of prayer. A red and white bouquet sat in Awad's place in the parliament chamber. Empty seats outnumbered people, though, as lawmakers took the podium one after another to denounce the bombing. One MP had his arm in a sling and a woman lawmaker wore a neck brace.

"The more they (terrorists) act, the more solid we become. When they take from us one martyr, we will offer more martyrs," Vice President Adil Abdul-Mahdi said. "The more they target our unity, the stronger our unity becomes."

But the turnout was low because of a weekly Friday ban on driving.

"Also the MPs' turnout is very low today because most of them are visiting those who were wounded by the blast," said Mohammed Abu Bakr, head of the parliament's media office.