Twelve of the dead were killed in separate attacks in Baghdad where US and Iraqi forces are involved in a major crackdown to curb the daily bloodshed.

In the deadliest attack, five soldiers and four Iraqis, including an interpreter, were killed on Thursday when a roadside bomb exploded near their vehicle during combat operations in northeastern Baghdad.

One soldier and two Iraqis were also wounded.

In northern Baghdad, one soldier was killed and three wounded when their vehicle was attacked by a rocket-propelled-grenade.

On Wednesday, four soldiers were killed when their convoy was struck by a roadside bomb in western Baghdad. Another soldier was wounded.

Two marines were killed in the restive western Anbar province on Wednesday.

And two more US soldiers were killed in southwest Baghdad and four wounded when a bomb exploded near their vehicle.

The latest fatalities took the military's losses in Iraq since the March 2003 invasion to 3,536, according to an AFP count based on Pentagon figures.

Earlier a suicide bomber exploded an oil tanker south of Iraq's oil-rich city of Kirkuk yesterday, killing 15 people and wounding 66, including policemen and local politicians.

The bomber blew up the tanker outside police headquarters and a cluster of government buildings in the town of Suleiman Beg, about 90km from the northern city of Kirkuk, police and hospital officials said.

"Several of the wounded are city council members and police officers, including the chief of police in Suleiman Beg, Hassan Ali Al-Bayati," a local hospital official said.

The attack came at 10:30 am (0630 GMT) and gutted the police headquarters and two local administration buildings, setting off fires near the blast crater, said a police officer from the nearby town of Tuz Khurmatu.

"Rescue efforts are still going on and they are still trying to put out the fires," said police Colonel Abbas Mohammed Amin, adding two of the dead and 18 of the wounded were policemen. The wounded also included two local politicians.

He added that most casualties had to be driven long distances for treatment, with the nearest hospital more than 20 kilometres from the blast site.

The latest attack -- two days after a Baghdad bomb killed 87 people -- was carried out as the US military pressed an air and ground assault on al-Qaeda strongholds north of Baghdad.

The military said by Thursday it had killed 41 people it described as insurgents and had destroyed some of their hideouts.

Around 10,000 US and Iraqi troops backed by attack helicopters and armoured vehicles have been battling alleged al-Qaeda militants in the restive province of Diyala since early Tuesday.

Dubbed Operation Arrowhead Ripper, the assault is viewed as the biggest since the November 2004 operation against the former rebel town of Fallujah and is aimed at destroying the group's strongholds in the province.

"Our combined forces have begun destroying al-Qaeda operatives and their resources in and around Diyala province," US commander Brigadier General Mick Bednarek said in a statement released overnight into Thursday.

The forces destroyed three "enemy safe houses" and a number of roadside bombs, it said, adding ground forces also found a house booby-trapped with homemade explosives in the Khatoon neighbourhood near Baquba.

The military said air support was called to destroy the house but a bomb missed its target and struck another nearby structure wounding 11 civilians.

The original target was later destroyed with missiles which produced a "large secondary explosion confirming the house as containing a large amount of explosives", it said.

Ethnically-mixed Diyala and its provincial capital of Baquba have emerged as hotbeds of al-Qaeda since Iraq's sectarian conflict broke out in earnest in February 2006.

The US military says it expects its onslaught to trigger a counter-attack from the group.

Speaking to The Times of London from Baghdad, General David Petraeus, the chief of US forces in Iraq, said on Wednesday that the network was "obviously going to have a surge of their own.

"You saw an example of this yesterday (Tuesday)," he said, referring to the massive truck bomb in Baghdad.

The military has lost one soldier in the operation since Tuesday, and on Thursday it announced the deaths of two more servicemembers in a roadside bomb attack in Baghdad.

The latest fatalities raised the military's losses in Iraq to 47 this month and to 3,524 since the March 2003 invasion, according to an AFP count based on Pentagon figures.

The military also said that more than 60 suspected insurgents were captured and their 17 boats destroyed in a separate operation southeast of Baghdad.

Insurgents fired about three mortar rounds on Thursday onto Baghdad's heavily-fortified Green Zone, the seat of the Iraqi parliament and site of the US and British embassies. No casualties were reported.

South of Baghdad, a local representative of radical Shia cleric Moqtada al-Sadr and his bodyguard were shot dead on Thursday in the town of Iskandiriyah, a police official said.