Alison Chung, Sky News Online

Dozens of bomb and mortar attacks have hit polling stations in Iraq killing at least 20 people as voting in parliamentary elections gets under way.

A volley of mortar attacks in western Baghdad killed at least seven people as polling stations opened, police officials said.

Also in the Iraqi capital, at least 12 people died after an explosion flattened an apartment block and four others were killed in a bomb blast at another residential building.

Mortar attacks also rained down on the heavily-fortified Green Zone that houses the Iraqi parliament, several ministries and the US and British embassies in Baghdad.

The violence comes despite a massive security operation in place for the elections, with 200,000 police and soldiers deployed in Baghdad alone.

Baghdad security spokesman, Major General Qassim al Moussawi, said most of the rockets and mortar bombs had been fired from mainly Sunni districts.

“We are in a state of combat. We are operating in a battlefield and our warriors are expecting the worst,” he said.

On Friday, al Qaeda threatened to kill voters, days after dozens died in a series of suicide attacks and bombings.

The Islamic State of Iraq, the al Qaeda front in the country, said today it was imposing a “curfew”.

Anyone who dared defy it would “expose himself to the anger of Allah and… all kinds of weapons of the mujahedeen,” the group said.

But tens of thousands of Iraqis have braved the dangers to queue up at polling stations to cast their votes.

As mortars landed several hundreds metres away in Azamiyah, Walid Abid, a 40-year-old father of two, said: “I am not scared and I am not going to stay put at home.

“We need to change things. If I stay home and not come to vote, Azamiyah will get worse.”

It is the second time Iraq has held elections since the 2003 US-led invasion and nearly 19 million Iraqis are expected to vote.

The US hopes the election will bolster Iraq’s fledgling democracy and pave the way to a smooth pull-out of American troops by the end of next year.

Shi’ite cleric Moqtada al Sadr, speaking at a rare news conference in Iran, said holding elections under the “shadow of occupation” was illegitimate.

However, he urged Iraqis to vote anyway to pave the way for “liberation” from US forces.