An al-Qaida-linked group yesterday claimed responsibility in an Internet posting for Thursday's suicide attack inside Iraq's parliament building.

The self-styled Islamic State in Iraq said, "a knight from the state of Islam ... reached the heart of the Green Zone ...blew himself up among a gathering of the infidel masters."

The statement is posted on an Islamist website usually used by insurgents. The authenticity of the statement could not been verified.

On Thursday, a suicide bomber managed to sneak into the heavily fortified Green Zone in central Baghdad and blew himself up in the Iraqi parliament complex.

The suicide bomber wearing an explosive vest detonated in a restaurant inside the parliament complex while many parliament members were having lunch, killing eight people, including three lawmakers, and injuring 23 others.

U.S. and Iraqi authorities have launched an investigation into the worst security breach in the Green Zone as many suspect that this attack was an "inside job."

Three workers in the restaurant have been detained for questioning, a senior lawmaker said on Friday. Some parliamentary guards were also being investigated but none were being held, according to media reports.

Members of the Iraqi parliament reconvened a special session Friday to condemn a suicide bombing in "a challenge against all the terrorists who want to stop the democracy process in Iraq" as stated by Parliament Speaker Mahmud al-Mashhadani.