Al-Qaeda's umbrella group in Iraq claimed responsibility Thursday for co-ordinated Baghdad bombings this week that killed 127 people and wounded more than 500, warning of more strikes to come against the Iraqi government.

The group, known as the Islamic State of Iraq, said in a statement posted on the internet that the attacks in the Iraqi capital targeted the "bastions of evil and dens of apostates."

It also warned the group is "determined to uproot the pillars of this government" in Iraq and said "the list of targets has no end." The authenticity of the statement could not be independently verified, but it was posted on a website commonly used for militant messaging.

The blasts Tuesday were the third major strike against government sites in the Iraqi capital since August, raising serious questions about the abilities of Iraqi security forces ahead of next year's national elections and the withdrawal of U.S. combat troops.

Al-Qaeda's claim gave renewed emphasis to U.S. military warnings that insurgents would likely continue high-profile attacks in an attempt to destabilize the Iraqi government in advance of the March 7 parliamentary elections.

The claim of responsibility came as Prime Minister Nouri al-Maliki was to face questions from lawmakers during a special session in parliament, where legislators have demanded answers over security lapses that allowed the attacks.

It appeared, though, that al-Maliki's top security chiefs would stay away. The prime minister arrived at the parliament Thursday without his interior and defence ministers, despite calls by lawmakers they appear as well to answer questions. The ministers have previously refused to attend two other sessions called after bombings on Aug. 19 and Oct. 25. More than 250 were killed in those attacks.

Lawmakers were scheduled to hold the special session behind closed doors with al-Maliki, who met first with the parliament speaker.

Al-Maliki signalled the beginning of a possible security shake up late Wednesday after replacing the military chief in charge of Baghdad security.

It was unclear whether the prime minister would announce any more changes in the leadership, although he has said Iraq's security strategies would be reviewed and further possible changes made.

Iraq has claimed al-Qaeda and loyalists of Saddam Hussein's Baath party operating from Syria were behind the massive strikes in August and October, as well as the most recent bombings. Relations between the two countries soured after Baghdad accused Syria of harbouring senior Baathists who masterminded the attacks. Syria has denied it.

The U.S. military did not immediately respond to an Associated Press request for comment on the validity of the al-Qaeda claim.

But the U.S. has said the August and October strikes bore the signature of al-Qaeda, known for suicide and vehicle-rigged bombings designed to inflict huge casualties that have tried to fuel sectarian tensions and push the country back to the Sunni-Shia violence of 2006 and 2007 that brought Iraq to the brink of civil war.

The three massive strikes in the Iraqi capital have differed from previous attacks because they hit government symbols and appeared aimed at having a far-reaching political impact, further undermining the government.