"We received two bodies completely burned and 13 wounded, six of them from the police and seven civilians," a doctor at the general hospital said, referring to the first attack, a car bombing which police said took place as a US-Iraqi patrol was passing on Thursday.

  

The second attack - a short time later, in western Samarra - targeted a police station but claimed no victims except the bomber, police said.

  

A third bomb exploded and injured an Iraqi guardsman while police were inspecting the area near the second attack, officers said.

  

The blast occurred after US forces had used loudhailers to warn Samarra residents to stay indoors.

 

A series of car-bomb attacks and clashes between US and Iraq troops and fighters in the town 120km north of Baghdad in early November left 36 dead, 26 of them police officers.

 

Baghdad blast

  

In Baghdad, a loud explosion rocked the central part of the city in Thursday and Reuters correspondents saw smoke rise from an area north of the Green Zone government complex.

   

Local residents in the west of the city also reported several loud explosions close to the airport.

   

An oil pipeline north of Baiji was
reportedly damaged by a blast

It was not clear what caused the blasts. An explosion two hours earlier had sent a heavy plume of smoke above the Green Zone. A US military spokesman offered no explanation.  

 

Baghdad airport is the main US military base in Iraq.

 

Thousands of troops were celebrating the Thanksgiving holiday with turkey dinners in the base canteen.

 

Pipeline attacked

 

Elsewhere, a key pipeline linking Iraq's northern oil fields to a major refinery was attacked on Thursday despite the deployment of a 2000-strong force to protect it, a local oil official said. The claim was denied, however, by the Iraqi national guard.

  

"A large blast caused by explosives damaged the pipeline in the Fatha area, 15km north of Baiji," refinery official Majid Mannun said.

 

"The blast has stopped the flow of crude to the refinery" which provides power to large swathes of northern and central Iraq, he said.

 

Diplomat slain

 

Also on Thursday, a group linked to Abu Musab al-Zarqawi said it had killed in Baghdad a US State Department official who worked with the Iraqi Education Ministry.

  

An Islamist website carried a statement in which al-Zarqawi's group purportedly claimed the killing.

  

In a statement released late on Wednesday, US Secretary of State Colin Powell identified the diplomat as James Mollen, who had volunteered for service in Iraq a year ago.