An Al-Qaeda inmate who escaped from Iraq's Abu Ghraib prison led militants who killed his own brother and 10 others overnight, a general said on Thursday.
The attack was the first attributed to one of more than 500 former prisoners, including senior Al-Qaeda members, who escaped last month in a major security breach that analysts say may bolster militant groups.
On Wednesday night, a group of militants went to the house of a policeman in Tikrit, north of Baghdad, took him into the garden and executed him, army Staff Lieutenant General Abdulamir al-Zaidi told AFP.
The policeman's brother, an Al-Qaeda member whose name was not given, led the group of killers, apparently in revenge for being informing on.
The militants then bombed the house and left a car bomb at the scene which exploded after a crowd of people arrived, killing 10 and wounding 58.
Zaidi said a file indicated the policeman had informed on his brother, who was arrested three years ago for multiple bombings and killings and given two death sentences, but who escaped during a mass breakout in July.
Militants assaulted Abu Ghraib prison west of Baghdad and another in Taji, to the capital's north, on the night of July 21.
Officials said more than 500 inmates escaped and over 50 prisoners and members of the security forces were killed in the assaults, which were claimed by Al-Qaeda front group the Islamic State of Iraq and the Levant.
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The assaults and jailbreaks highlighted the growing reach of militants and the worsening security situation.
"The prison attacks demonstrate that the security forces are poorly resourced and unable to protect what should have been well-defended facilities," said John Drake, an Iraq specialist with risk management firm AKE Group.
"The release of inmates could also bolster the ranks of the militants and increase their capabilities, both in Iraq and in neighbouring Syria."
Violence killed almost 1,000 people in July, government figures show, making it Iraq's deadliest month since April 2008.
Attacks have markedly increased this year, especially since an April 23 security operation at a Sunni Arab anti-government protest site that sparked clashes in which dozens died.
Protests erupted in Sunni-majority areas in late 2012, amid widespread discontent among Sunnis who accuse the Shiite-led government of marginalising and targeting them.
Analysts say Sunni anger is the main cause of the spike in violence this year.
In addition to security problems, the government in Baghdad is also failing to provide adequate basic services such as electricity and clean water, and corruption is widespread.
Political squabbling has paralysed the government, which has passed almost no major legislation in years.