BAGHDAD, Dec 27: Thirteen people were killed on Monday when a suicide bomber attacked the headquarters of a top Iraqi Shia political leader, while the country's main Sunni Muslim party announced a boycott of next month's crucial elections.

Abdel Aziz al-Hakim, the head of the Supreme Council for the Islamic Revolution in Iraq (SCIRI), escaped with his life after the bomber rammed an explosives-laden car at his Baghdad office, killing 13 people and wounding scores more in a massive ball of flames.

"I heard a strong explosion and a fireball rose into the sky. There was smoke in front of their offices. We ran and I heard glass shattering. I saw several bodies being taken away in a pick up," said store owner Iyad Allawi.

His brother, Ayatollah Mohammed Baqer al-Hakim, the party's previous leader, was assassinated in a suicide car bomb attack outside a shrine in Najaf in August 2003. SCIRI spokesman Haitham al-Husseini blamed Saddam's old Baath party for the attack, saying: "It was elements of the old regime and other extremists trying to stop the political process in Iraq."

Hakim, who spent two decades in Iranian exile, heads a coalition that is expected to do well in the election, and almost certainly put the 60 per cent Shia majority in power after marginalisation under Saddam and before him.

It was latest attack against Iraq's majority Shia community, which was oppressed under ousted dictator Saddam Hussein but is expected to win power in the Jan elections. Iraqi Islamic Party leader Hamid condemned the bombing as an attempt to divide Shias and Sunnis. It came eight days after twin car bombs in the main Shia holy cities.

Hakim is the top candidate in the Shia coalition grouping called the Unified Iraqi Alliance, which is the early election favourite due to its endorsement from Grand Ayatollah Ali al-Sistani, the most revered Shia cleric in all of Iraq.

But in a major blow to US and Iraqi government efforts to attract a strong role of the once-dominant Sunni Muslim minority in the elections, the community's main party announced it would not be taking part.

The country's foreign minister had raised the possibility of delaying the vote in trouble spots around central Iraq before the Iraqi Islamic Party dropped its political bombshell.

"We are obliged to pull out," party chief Mohsen Abdel Hamid told reporters, saying the decision was motivated by the refusal of authorities to postpone elections for six months to ensure broader participation.

"Our party asked on December 5 that elections be delayed for six months using reasonable arguments," he said referring to the worsening security situation in the country in the run-up to the vote as a result of a mainly Sunni-led insurgency.

"The authorities concerned have refused to hear the voice of reason." The party had previously presented an election list of 275 names, a number equal to the seats up for grabs in the national assembly.

Abdel Hamid left the door open for a change of heart, saying his party would reconsider if certain conditions were met including an improvement in the security situation and more public awareness of the vote.

With the pullout of the Iraqi Islamic Party, the Sunni field would essentially be represented by the party of senior politician Adnan Pachachi and some independent figures.

The Iraqi Islamic Party represented the best chance to endow the next government with legitimacy among Sunnis after their religious establishment led by the influential Committee of Muslim Scholars called in November for a mass boycott of the elections.

Since the fall of Saddam in April 2003, the Sunnis who make up 20 per cent of the population have expressed ambivalence over Iraq's new political order dominated by the Shia majority.

Monday's car bomb shook southern Baghdad in the early morning, sending thick clouds of dark smoke into the air. Grand Ayatollah Sistani has issued a religious edict obliging all Shias to vote in the poll, a move that is likely to boost turnout and favour Shia parties.

That has led to concerns among Iraq's 20 per cent Sunni Arab minority that they will be marginalised at the ballot box, particularly since most of the violence sweeping the country is in Sunni Arab areas to the north and west of Baghdad.

Last month, Sunni Arab groups, including the Iraqi Islamic Party, called for the poll to be delayed by up to six months, arguing that there was no way it could be free and fair amid the mayhem. The Electoral Commission rejected that request.

The Commission has also dismissed a suggestion, attributed to US officials and floated in the New York Times on Sunday, that Sunnis might be given extra seats if the vote is skewed. But Washington, which has a reinforced army of 150,000 in Iraq for the election, is clearly working hard behind the scenes to ensure a vote that would produce the kind of legitimate government that can provide its forces with an exit strategy.

US and Iraqi officials have warned of an increase in violence in the run-up to the election, which will see the creation of a 275-seat national assembly and a new government. -Reuters/AFP