An al-Qaeda-linked group has claimed responsibility for a coordinated suicide bomb and gun attack on the country's justice ministry last week that killed at least 18 people.
Islamic State of Iraq (ISI), an umbrella group for al Qaeda-linked fighters, said in a statement published online on Sunday that it had ordered the suicide bombers to attack the building floor by floor and "liquidate" its enemies inside.
"In a blessed raid among a series of operations for revenge... Baghdad's knights undermined another vicious bastion which was always a tool against Sunnis, torturing, terrifying, imprisoning and executing them," the group said in the statement.
The assault near the heavily fortified Green Zone, where several Western embassies and government offices are located, fanned fears about Iraq's still fragile security a decade after the US-led invasion ousted late President Saddam Hussein.
"Baghdad's knights undermined another vicious bastion which was always a tool against Sunnis, torturing, terrifying, imprisoning and executing them."
- Al-Qaeda, online statement
Three car bombs exploded and a suicide bomber blew himself up in broad daylight in the heart of the capital on Thursday.
Another suicide bomber then walked into the justice ministry and set off his device while armed men attacked the building. Iraqi security forces eventually regained control.
Overall, at least 18 people were killed and more than 30 wounded, security and medical officials said. But ISI claimed to have killed 60 people, according to a statement distributed by the SITE monitoring service on Sunday.
Iraq's power-sharing government has been all but paralysed since US troops left more than a year ago. Prime Minister Nuri al-Maliki, a Shia, is facing protests in the country's Sunni heartland, which shares a porous border with Syria.
Violence has intensified as Sunni opposition protests have swelled and Iraq's al-Qaeda affiliate has urged the protesters to take up arms against the government.
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Britain-based Iraq Body Count (IBC), meanwhile, published a study which concluded that at least 112,000 civilians have been killed in the 10 years since the invasion of Iraq.
It said that, including combatants on all sides of the decade-long conflict as well as yet undocumented fatalities, the figure could rise as high as 174,000.
IBC said that, over the years, Baghdad had been, and still is, the deadliest region, accounting for 48 percent of all deaths, while the conflict was bloodiest between 2006 and 2008.
It noted that violence remains high, with annual civilian deaths of between four and five thousand - roughly equivalent to the total number of coalition forces killed from 2003 up to the US military withdrawal in December 2011, at 4,804.
Iraq's military and police are persistently described by Iraqi and US officials as capable of maintaining internal security, but are unable to protect the country's borders, airspace and maritime territory.
But attacks such as the March 14 assault remain common, in addition to a vast array of shootings and bombings nationwide, killing hundreds of people on a monthly basis.