Fuel riots and more than a dozen car bombs greeted the New Year in Iraq Sunday as relatives celebrated the release of one Cypriot and five Sudanese hostages by their captors.
At least 40 people were killed in the wave of bombings, which struck the tense northern oil city of Kirkuk and towns just north of the capital as well as Baghdad itself, security officials said.
Insurgents also shot dead a policeman in the main northern city of Mosul and wounded two more in a roadside bombing to its east.
The US military confirmed a soldier had been killed in a New Year's Eve mortar attack in south Baghdad, bringing its losses for 2005 to at least 844, according to the Iraq Coalition Casualty Count, a non-profit organisation that tracks the dead and wounded.
The death toll was very slightly down on the 848 recorded in 2004.
More than 30 soldiers from other coalition countries also died in Iraq in 2005.
Overall US losses since the 2003 invasion reached at least 2,175, according to an AFP count based on Pentagon figures.
An estimated 30,000 Iraqi civilians have been killed over the same period, according to Iraq Body Count, an independent organisation that monitors media reports.
In Kirkuk, persistent fuel shortages in the oil city sparked rioting in which one person was killed and four wounded, prompting the authorities to impose an overnight curfew.
Protestors torched two petrol stations and a building housing offices of the state oil company as well as police vehicles, an AFP correspondent witnessed.
Stonethrowing demostrators in the mainly Kurdish Rahimawa neighbourhood of the city also seized some police weapons.
US helicopters hovered overhead but ground troops stationed not far away did not intervene.
Police commander Brigadier-General Munis Isahak said the authorities had had no choice but to impose a 12-hour curfew in a bid to restore order.
"The citizens have a right to protest but these have turned violent and people have been hurt," he said. "A lot of our vehicles have been damaged."
Fuel supplies to a vast swathe of northern and north-central Iraq have been badly hit by a 10-day-old action by truck drivers at the region's main oil refinery in the town of Baiji to protest death threats from Sunni Arab insurgents.
In a separate protest in the southern oil centre of Basra, at least 1,000 people burned tyres to protest increases in pump prices.
In a new assault on oil infrastructure, insurgents blew up a pipeline near the Dura refinery in south Baghdad, sparking a major blaze and further hitting output of petrol and other refined products.
"This attack has affected production at the refinery, which can handle 110,000 barrels a day, but it has not stopped production," said oil ministry spokesman Assim Jihad.
The spokesman said a few deliveries of refined products had resumed from Baiji after some of the striking drivers returned to work.