BAGHDAD - Iraqi officials stepped up security Monday ahead of a major Shiite pilgrimage after a mortar attack on a religious procession in Baghdad killed seven people and wounded dozens.

The attack came during a sectarian-fueled deadlock in Iraq's Shiite-led coalition government and may further inflame tensions.

Security forces have been put on high alert and new measures have been taken to prevent attacks on the tens of thousands of pilgrims expected to gather to commemorate the death of a revered imam, said Dhia al-Wakil, a spokesman for the Defence Ministry and the Baghdad operations command.

Prime Minister Nouri al-Maliki issued a warning Monday against "attempts to exploit religious events and pilgrimages" through militant displays — a remark apparently aimed at firebrand Shiite cleric Muqtada al-Sadr, whose followers have been known to take to the streets in shows of force.

Pilgrims have already started to arrive in Baghdad for the commemorations marking the eighth century death of Imam Moussa ibn Jaafar al-Kadhim, one of the 12 principal Shiite saints, who is buried in a mosque in the northern neighbourhood of Kazimiyah.

Two mortar shells hit a procession in Kazimiyah late Sunday, killing seven and wounding 38. The attack came before the expected climax of religious observations on Saturday, when pilgrims traditionally walk to the twin-domed shrine in Kazimiyah where al-Kadhim is said to be buried.

On Monday, all side streets in Kazimiyah and its surrounding areas were blocked to secure the way for pilgrims, an Interior Ministry official said, speaking on customary condition of anonymity.

The al-Kadhim procession was struck by tragedy in 2005, when thousands of Shiite pilgrims panicked by rumours of a suicide bomber broke into a stampede on a bridge, leaving some 1,000 of them dead. Police later said no explosives were found on the bridge, and poor crowd control and the climate of fear in Iraq appeared largely to blame.

Officials said Sunday's attack, like many of the bombings that still plague Baghdad and the rest of Iraq, was intended to stir up animosity between Iraq's Shiite and Sunni Muslims, the two largest religious groups.

A director of an intelligence cell in the Baghdad operation command blamed al-Qaida for the mortar attacks, saying the terrorist movement's hallmark is to hit the Shiites to provoke a reaction from them against Sunnis. He said similar attempts at attacks were expected, and the government has deployed ground forces accompanied by air cover. He also spoke on condition of anonymity.

The attack came the same day as an attempt to push Shiite Prime Minister Nouri al-Maliki out of office failed. The country's president refused to ratify a petition for a no-confidence vote in parliament because it lacked the needed number of signatures.

At the root of the standoff is the unresolved power struggle among Iraq's three main groups — the majority Shiites and minority Sunnis and Kurds — following the ouster of Saddam Hussein in the U.S.-led invasion of 2003. The continued impasse after the last American troops withdrew in December has raised the possibility of renewed sectarian violence and hampered plans for rebuilding the country.

Al-Maliki, a Shiite, is under fire for breaking promises to share power with his partners in a unity government that includes the Sunni-dominated Iraqiya bloc, Kurdish parties and loyalists of Shiite cleric al-Sadr.

Critics say al-Maliki has been consolidating power among security forces and in the judiciary, and Sunnis believe he is targeting their leaders with politically motivated prosecutions.

On Monday, al-Maliki chaired a meeting of senior security leaders, and his website warned against militant demonstrations ahead of the upcoming pilgrimage.

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Additional reporting by Associated Press writer Qassim Abdul-Zahra.

News from © The Associated Press, 2012