Insurgents hit back with a double car-bombing, one to the north and another to the south of Baghdad, that left four people dead and dozens wounded, while two local Iraqi leaders were gunned down in separate attacks.

The relentless violence prompted relief agency Doctors without Borders to announce it was pulling its staff out of the country.

But Prime Minister Iyad Allawi, on a trip to Europe, called on all countries -- including those opposed to the US-led war which toppled Saddam Hussein last year -- to help build a new Iraq.

Analysts said Bush's victory in the presidential race increased the chances of a violent showdown between US troops and rebels over the flashpoint city of Fallujah, the suspected hideout of Al-Qaeda operative Abu Musab al-Zarqawi and his followers.

US planes bombed rebel positions in the Sunni Muslim bastion overnight, the US military said, while violence also flared in nearby Ramadi.

Thousands of families have already fled the city, 50 kilometres (30 miles) west of Baghdad, where US ground troops have massed since mid-October.

"US troops will enter Fallujah, Latifiyah, Ramadi and Qaim all at once in the next few days after Bush's re-election," said Mohammed al-Askari, a former Iraqi army officer turned political analyst, referring to other flashpoints.

US and Iraqi officials are desperate to crush the insurgency ahead of national elections planned for January, and have threatened force if necessary.

"These elections are important," Bush said in his first post re-election news conference in Washington, vowing to ensure commanders on the ground in Iraq would receive extra troops if necessary to "complete their missions".

For his part Allawi, on a trip to Europe, took a stab at France and Germany, urging "spectator" countries to get involved in stabilizing his country.

"I want to take this opportunity to call on the countries which are content to have a spectator role to help us to build a better Iraq," he told reporters on the eve of an EU summit in Brussels.

The situation in Iraq could not be resolved "without the help of all the important countries".

France and Germany strongly opposed last year's invasion and have refused to send troops to join the US-led coaltion in Iraq. Hungary said Wednesday it would withdraw its 300-troop contingent from the country at the end of March.

Insurgents have waged a bloody campaign of bombings and kidnappings in a bid to derail the election process and undermine the interim government.

At least four Iraqis were killed and 18 wounded when a car bomb exploded on Thursday morning outside a city council building north of Baghdad, while a second car bombing to the south wounded six Iraqi national guards.

A car sped towards the building in Dujail, a city 50 kilometres (30 miles) from the Iraqi capital, said US military spokewsoman Cynthia Weasner. "It detonated in front of the building."

A second car laden with explosives exploded near a checkpoint in the restive town of Iskandariyah, wounding the national guards.

In a separate attack northest of the Iraqi capital, unknown assailants shot dead Jassem Ali, who heads the village of Heb Heb, and wounded two of his bodyguards.

In Ramadi, meanwhile, the head of a powerful local tribe, Sheikh Khamis Futaikhan, was gunned down in an ambush on his car.

Time was fast running out for kidnapped aid worker Margaret Hassan after her unknown kidnappers threatened to deliver the British-Irish woman to Zarqawi by a Thursday deadline unless Britain pulled its troops out of the country.

The 59-year-old, who is married to an Iraqi and is the Iraq director of relief agency CARE International, has been held hostage since October 19. The agency has since closed its operations in Iraq.

In a further blow to Iraq's rehabilitation, Doctors without Borders (Medecins Sans Frontieres - MSF) said it was pulling out of Iraq because of escalating violence and the danger to its staff.

Meanwhile, a body suspected to be that of an Iraqi man was found in the northern city of Kirkuk, police said, adding that the victim had been blindfolded and shot to death, most likely for collaborating with US forces.

As preparations for Iraq's polls gather steam amid the relentless violence, election organisers announced that Iraqis living abroad would be allowed to vote, ending months of debate over the thorny issue.