The Baghdad workers turned out to protest on Tuesday after hearing the Americans had detained a woman for refusing to be searched by a sniffer dog. There were no immediate reports of injuries.

A Reuters correspondent said US soldiers fired in the air on Tuesday to disperse a furious crowd at a complex of government buildings in Baghdad. The complex includes the oil, electricity, trade and irrigation ministries.

Dogs are widely regarded as religiously "impure" animals across the Middle East and being searched in this way is seen as culturally offensive by Iraqis.

An incident involving a dog searching a woman is especially sensitive. But the US army in Iraq has nevertheless continued the practice.

US military spokespeople were not immediately available for comment.

Mortar attack

Elsewhere, in northern Iraq, a US base in the district of al-Qala, south of the town of Samarra, came under a mortar attack early on Tuesday, Aljazeera’s correspondent reported.

Locals said they saw columns of smoke rising from the scene while US helicopters flew over the area.

In another incident, a fire broke out late on Monday after an explosion hit a gas pipeline linking Biji to al-Haditha area, north of Baghdad, the correspondent reported.

US helicopters flew over the area immediately, he added.

US death

US military sources announced the death of a soldier, apparently from an "accidental explosion" in Camp Anaconda near Baghdad.

"The soldiers were inflating the tyre of an aircraft when either the tyre or nitrogen exploded," a military spokeswoman announced.