A suicide bomber killed at least 29 people today by driving an explosives-laden vehicle into a Shia Muslim funeral procession in Baghdad, heightening fears that Iraq is in the grips of sectarian conflict.
There was no immediate claim of responsibility for the attack in the capital's predominately Shia district of Zafraniya, which also wounded more than 60 people, but it came just days after al Qaeda's Iraqi affiliate pledged to step up attacks on the country's Shia majority.
The majority of the dead were mourners who had gathered for the funeral of a Shia estate agent, killed with his wife and son the previous day when gunmen stormed into his shop. That attack was also assumed to have sectarian overtones.
More than 200 people have been killed since US troops completed their withdrawal from Iraq at the end of last year, 87 of them this week alone, according to news agency tallies.
The surge in violence comes against the backdrop of a political crisis that has seen Nouri al-Maliki, Iraq's Shia prime minister, take controversial steps to neutralise some of the most powerful Sunni Arab challengers in his coalition government.
On Mr Maliki's orders, police attempted to arrest Tareq al-Hashemi, the popular vice president, on suspicion of running a death squad. Mr Hashemi has since fled to relative safety in the Kurdish north. The prime minister also attempted to dismiss Saleh al-Mutlaq, his Shia deputy.
Militants linked to al Qaeda have taken advantage of Sunni anger and a security vacuum left by the departure of US forces to launch a series of bombings, prompting reprisal attacks by Shia militias. Seven residents of Baghdad's Sunni suburbs were among 26 people killed countrywide on Thursday.
But there have also been worrying signs that political score-settling has taken on a more violent hue, adding to the increasingly calamitous atmosphere gripping the country.
A series of fatal drive-by shootings in recent weeks have targeted checkpoints manned by members of Sunni militia known as the Sawha.
Sahwa irregulars make up part of the Sunni Awakening, a potent coalition of tribal militias that sided with the United States against Al Qaeda in 2006 and made a vital contribution in stemming an insurgency that had threatened to tip Iraq into a full civil war.
Sensing a dangerous rival, Mr Maliki demanded that the Awakening disband its militias and disarm the 80,000 men serving in them by the end of last month. Iraq's Shia politicians have long feared that without the buffer provided by US troops the Sunni Awakening could emerge as a separate armed forces, challenging the primacy of the regular army and police.
But the resurrection of Sunni-Shia tensions has made tribal leaders in western Iraq, the Awakening's main stronghold, even less likely to countenance a disbandment of their community's best form of security. So far they have shown no sign of heeding Mr Maliki's ultimatum.
Shia government officials have blamed Al Qaeda, the Awakening's old enemy, for the attacks on the Sahwa militia, but many Sunnis remain suspicious of such explanations.
Although suspicions are also directed to Al Qaeda militants for a growing number of attacks on regular army and police checkpoints, some in Iraq have concluded that the Sawha is now retaliating. If true, such reprisals would represent a further alarming development in a country that seems more febrile than at any time in the past five years.