Police and health officials in Iraq said a blast that killed two targeted pilgrims walking to the holy Shia city of Karbala to commemorate Arbaeen, the end of 40 days of mourning following the anniversary of the death of Imam Hussein, a revered Shia figure. The attack took place in the Baghdad suburb of Awairij. The officials spoke on condition of anonymity because they were not authorised to brief the media.

Iraqi leaders are locked in a political standoff that began after the Shia-dominated government called for Sunni Vice President Tariq Al-Hashemi's arrest on terrorism charges just as the last American troops were leaving last month.

The standoff is at the heart of an ongoing political crisis pitting the leaders of the country's mostly ethnic- and sectarian-based party blocs against each other. Iraq's Sunni minority dominated the government under the dictatorship of Saddam Hussein.

US and some Iraqi officials have warned of a resurgence of Sunni and Shia militant activity after the US troop withdrawal. Also Monday, an Al-Qaida front group in Iraq claimed responsibility for a November bombing inside Baghdad's Green Zone, a heavily protected area in the center of the Iraqi capital.

Iraqi Prime Minister Nouri Al-Maliki described the Green Zone bombing near parliament as an assassination attempt against him. The claim of responsibility by the Sunni militants said the suicide attack was targeting "the head of the Iranian project in Iraq," an apparent reference to Al-Maliki and the ties of Iraqi Shias to Shia-majority Iran. The statement said the attack failed because the car exploded prematurely.

"A hero driving a car bomb was able to penetrate all security measures in the Green Zone," said the statement in the name of the Islamic State of Iraq. "The operation was not completed due to a technical problem and the car exploded while parked at the entrance of the parliament."