A key adviser to the newly-installed Iraqi Government was among at least ten people killed and hundreds injured today as violence escalated in response to a crackdown on the insurgents.

Wael al-Rubaei, an aide to Prime Minister Ibrahim al-Jaafari's Cabinet, was ambushed and shot dead as he was driven to work in the central Mansour zone of Baghdad this morning. His driver was also murdered.

The terrorist group run by Jordanian Abu Musab al-Zarqawi, claimed responsibility for the assassination in an unverified statement posted on an internet site.

Earlier, a suicide bomber killed five people and wounded 13 when he drove a pick-up truck packed with explosives into a crowd gathered outside a council office in Tuz Khormato, 55 miles south of the northern city of Kirkuk.

And at least four people were killed and more than 110 injured in a car bomb attack outside a Baghdad restaurant popular with police officers in the Shia-dominated Talibia district of the capital.

The bomb, outside the Habayibna restaurant in the capital's Shia-dominated a district, exploded at 2.15pm (11.15 BST) as local police officers met there for lunch.

Security sources described how the vehicle was parked in front of the cafe and detonated by remote control. Several parked cars were ablaze and a frantic rescue effort was underway to free survivors from the wreckage.

A copy of the Koran was reportedly found intact in the shell of the burned-out vehicle.

The upsurge in violence takes the number killed since the Shia-led coalition Government was installed a month ago to more than 550.

Today's attacks coincided with Operation Squeezeplay, a sweep of the capital's western suburb of Abu Ghraib. US troops, who oversaw the operation which was primarily undertaken by the Iraqi police, said that there had been 285 arrests.

"This is the largest combined operation with Iraqi security forces to date," said US military spokesman Lieutenant Colonel Clifford Kent.

Richard Beeston, Diplomatic Editor of The Times in Baghdad, said that the fragile Government's reaction to today's violence was being closely watched by the Iraqi people, who are losing patience with its inability to stamp out the insurgency.

He said: "There is a lot of pressure on the Government to persuade people that it is up to the job. People are not convinced that the new Government actually means very much or that it has a great deal of power.

"In the past two days we have seen a rush of high-profile press conferences and raids on insurgency strongholds. The TV stations were all covering the raids in Abu Ghraib. The message that the Government is trying to get out is that it is aware of the seriousness of the situation and is getting it under control.

"On the other hand, we have the insurgents continuing to do what they do best - blowing things up. Today we had the bomb on the restaurant in a predominantly Shia area, the assassination of a key government adviser and other attacks up and down the country.

"The difference is that we are now seeing the Government responding. At the weekend in the town of Kut, south of Baghdad, death sentences were handed out to three insurgents. The Government has made it clear that it will continue to sentence people to death and it wants to show that it is getting tough.

"On the political level, however, it faces an even more difficult job. The Government needs to build a consensus and separate the political process from the ongoing violence. They need the Sunni minority to come on board so that they can draw up a constitution.

"They have made some advances in this but it is still early days. I think in the coming weeks we are going to see a lot more raids and a lot more bombs."

Meanwhile, three Romanian journalists were expected to return home today after they and their Iraqi-American guide were released after being held captive for nearly two months.

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