A suicide truck bomber smashed his way into a police complex in Iraq's restive northern city of Mosul on Tuesday before blowing the vehicle up and killing seven people, police said.

Among the dead in the early morning attack in the Al-Bid district of central Mosul were four policemen, said Captain Ahmad al-Sabbawi.

Another officer said 17 police were among 38 people wounded in the blast.

"The suicide bomber tried to enter from the rear (of the complex) but police opened fire and his vehicle crashed into the concrete protection barrier before blowing up," said local police commander Ismail Ahmad.

The police post was badly damaged.

"I fell out of the watch-tower because of the strength of the explosion. I broke my leg and have injured a shoulder," one of the wounded, Saad Fathi, said from his hospital bed.

The attack in the country's second largest city was similar to dozens of others carried out by al-Qaeda, for whom Mosul is their last urban stronghold in Iraq, according to US military commanders.

On Sunday, 15 people were wounded in a car bomb attack at a marketplace in Al-Gayara, near Mosul.

Despite repeated US-Iraqi operations in Mosul, the city remains under the influence of insurgents and rebels, in part due to a complex Kurd, Sunni and Christian mix but also because of tribal loyalties.

Mosul was plunged into violence in 2005, which intensified when al-Qaeda militants took refuge in the city of more than 1.5 million people after being chased out of Baghdad and the western province of Anbar in 2007.

The Iraqi military itself has been on the offensive in Mosul since May 2008 but has so far failed to halt the deadly attacks.

Although the number of insurgent strikes has eased over the past year, Nineveh province, of which Mosul is the capital, and Diyala province, northeast of Baghdad, remain the most dangerous areas of Iraq.

A US military commander acknowledged last week that the insurgency in Mosul has been weakened but not defeated, posing a challenge for Washington as US troops prepare to withdraw.

A military pact signed last year between Baghdad and Washington stipulates that US soldiers pull out of Iraqi cities by the end of June.

"We are not sure what will happen after 30 June. That is for senior officials to decide," said Colonel Gary Volesky, the chief US commander in Nineveh province.

US President Barack Obama last month ordered an end to American combat operations in Iraq by August 2010, ahead of a complete withdrawal the following year.

A reminder of al-Qaeda's ability to strike in Mosul came in early February when a suicide bomber aboard a car killed US Lieutenant Colonel Gary Derby, a 1st Cavalry Division commander.

But on 25 March, a US military spokesperson said the number of attacks countrywide had dropped to its lowest level since the months which followed the 2003 invasion that toppled Saddam Hussein.

"Attacks are at their lowest since August 2003," Major General David Perkins told reporters, adding that weekly incidents were as much as 90 percent down compared with June 2007.