An Iraqi activist was shot dead overnight in Baghdad, a police source told AFP on Thursday, as anti-government rallies carried on despite a separate day-long siege of the US embassy.

The activist, Saadoun al-Luhaybi, was shot in the head in a southwestern neighbourhood of the Iraqi capital, the police source said. He had been taking part in youth-led demonstrations rocking Iraq since early October that have demanded the ouster of a governing class seen as corrupt, inept and beholden to Iran.

The protesters have occupied Baghdad's iconic Tahrir Square, just across the river Tigris from the Green Zone, home to government offices, the United Nations headquarters and foreign embassies. On Tuesday, an angry mob marched into the Green Zone and to the US embassy, outraged over American air strikes that killed fighters from the Hashed al-Shaabi military force.

They besieged the embassy for just over 24 hours, leaving on Wednesday afternoon after an order from the Hashed. The anti-government demonstrators who have been taking to the streets for months insist their movement is entirely unrelated to the crowds that besieged and vandalised the American mission. "We've got nothing to do with that," one demonstrator in the southern protest hotspot city of Diwaniyah told AFP.