Al-Qaida's umbrella group in Iraq claimed responsibility for the double suicide bombing in the centre of Baghdad. At least 155 people, including 24 children, were killed in the blasts.
The al-Qaida branch, known as the Islamic State of Iraq, said in a statement posted on the Internet late Monday that its "martyrs ... targeted the dens of infidelity."
Massive car bombs have been the hallmark of al-Qaida and Sunni insurgents seeking to overthrow the country's Shiite-dominated government in Iraq.
The attack Sunday in the heart of the Iraqi capital struck the Justice Ministry and the Baghdad Provincial Administration. It was Iraq's deadliest attacks in two years and it raised more fears about the country's ability to protect itself as it prepares for January elections and the U.S. military withdrawal.
Among the dead were two dozen children, killed on a bus that was leaving a daycare center near the Justice Ministry at the time of the explosions, said an official at the hospital where the bodies were brought. The official spoke on condition of anonymity because he was not authorized to talk to the media, The Associated Press reports.
It was also reported, the attacks were the deadliest seen in Iraq in two years, targeting the justice ministry and the Baghdad provincial administration and raising fears about Iraq's ability to protect itself as it prepares for the US military withdrawal.
"The bloody Sunday explosions strengthen Iraq's demand to the UN and the Security Council to nominate a senior international envoy to come to Iraq and evaluate the degree of interference targeting stability in Iraq," Zebari told al-Arabiya television.
"I believe this will be achieved soon, especially after [Sunday's] explosions confirmed that this issue is vital and important. We need the help of the international community."
"The blood of Iraqis is very cheap and I ask, how many victims will it take to convince the government that it has totally failed?"
A spokeswoman for Ban Ki-moon, the UN secretary-general, said he was awaiting a response from the Security Council, Aljazeera.net reports.
Meanwhile, the militant group had pledged to wreak further havoc in a bid to destabilise Iraq's fragile government prior to a national election planned for 16 January.
Exposing the vulnerability of institutions has been a stated goal of al-Qaida, which the Iraqi prime minister, Nouri al-Maliki, has insisted is backed by figures from the Saddam Hussein regime.
Maliki inspected the scene of the attacks late on Sunday and vowed to find the perpetrators, blaming Syrian leaders for harbouring Ba'athists whom he said were directing a subversive campaign.
Iraq and Syria have been at loggerheads since August after Maliki partly blamed the Syrians for facilitating the summer attacks, guardian.co.uk reports.