The four bombs killed 127 people and wounded over 400
A militant group linked to al-Qaeda has said it carried out five connected suicide bombings in the Iraqi capital on Tuesday that left scores dead.
The Islamic State of Iraq posted the claim on a website used by militants, news agencies reported on Thursday.
The attacks on government-run buildings in Baghdad killed at least 127 people and wounded 400, according to police sources.
US Defence Secretary Robert Gates arrived in Baghdad on Thursday.
He is on an unannounced visit at a time when the US is making preparations to reduce its troop levels from next year.
Iraq's decision to hold parliamentary elections in March, a delay of several weeks from the original date, will not affect US plans to end combat operations next August and reduce the number of US troops to 50,000 from about 115,000 now, Mr Gates told the Reuters news agency.
The Islamic State of Iraq, an al-Qaeda affiliated group, claimed attacks in August and October which killed 240 people.
The statement, posted by a website forum contributor, said the bombings "targeted the headquarters of evil, the nests of non-belief".
DEADLIEST ATTACKS SINCE 2003
Mar 2004: 171 killed in bombings in Baghdad and Karbala
Nov 2006: 202 killed in multiple blasts in Baghdad
Mar 2007: 152 killed in truck bombing in Talafar
Apr 2007: 191 killed in car bombings in Baghdad
Aug 2007: More than 500 killed in attacks on villages near Sinjar
August 2009: 95 killed in truck bombs in Baghdad
Oct 2009: 155 killed in twin truck bomb attacks in Baghdad
Dec 2009: At least 127 killed in a series of car bombs in Baghdad
Source: News agencies, BBC
"The list of targets will not end," the statement said.
Prime Minister Nouri Maliki has arrived at a special session being held at the Iraqi parliament to to answer questions from lawmakers on how the bombers were able to get past security services to carry out the attack.
Iraq has claimed that former Baath party loyalists could also be responsible for the bombings.
Jihad al-Jabiri, head of the Interior Ministry's bomb squad, said the militants had backing from Syria, Saudi Arabia or another government.
On Wednesday Mr Maliki sacked the government's security chief for Baghdad because of the security failings around the bombings.
In previous attacks it has been suggested that the bombers had help from sympathisers inside the security services.