Iraqi Parliament bombing - A knight from the state of Islam.

An al-Qaida-linked insurgent group on Friday claimed responsibility for Thursday's deadly Iraqi Parliament bombing in Baghdad's Green Zone, according to Internet statements.

"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 in Iraq said in a statement posted on an Islamist Web site commonly used by insurgents.

U.S. officials said Friday one Iraqi civilian was killed in the suicide attack on the parliament cafeteria in the heavily fortified Green Zone compound. Iraqi officials said Mohammed Wad, a Sunni member of the moderate National Dialogue Front, was killed.

But the Islamic State in Iraq, which is an al-Qaida-led Sunni Muslim umbrella group, said the attack killed three lawmakers and seriously injured several others, according to the Internet statement.

The U.S.-based SITE Institute, which tracks militant postings, said the claim by the Islamic State appeared authentic.

The militant group said the attack "revealed the lies of the Baghdad security plan that they have been marketing to the international media ... as a way to save their face, which has been torn down by the arms of the soldiers of the Islamic state."

In a second Internet statement posted immediately after the first, the group said it scouted several locations and "after studying ... we managed to reach the most fortified location of the (Iraqi Prime Minister Nouri) al-Maliki government and the crusaders."

"The monkeys in parliament cried and screamed in horror at what they saw after an invading knight, a hero of the Islamic State ... entered among them to detonate his explosive belt among the gathering of apostasy known as the parliament. Through his hand, God destroyed a group of infidels and apostates," the second statement said.

The Islamic state said its claim was delayed because it wanted to allow its members to withdraw from the site before issuing the statement. It also pledged to conduct similar attacks in the future.

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 experts cast doubt on its authenticity.