After breaking a months-long jihadist siege of the Shiite Turkmen town of Amerli by Islamic State (IS) fighters, troops on Tuesday regained control of part of a key highway linking Baghdad to the north.
Two towns north of Amerli were also taken from the jihadists on Monday as Iraqi forces -- backed by US air strikes -- score their first major victories since the army's collapse across much of the north in June.
Demanding to know their fates, angry relatives stormed parliament in Baghdad, attacked MPs and began a sit-in in its main chamber, an official said.
Anti-riot police were trying to evict the hundreds of protesters, who were also calling for some officers to be held accountable, said the official, who was present at parliament.
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Concern over those in jihadist hands has been fuelled by reports of widespread atrocities, including accusations from Amnesty International of war crimes and ethnic cleansing.
The Sunni extremist IS declared an Islamic "caliphate" in regions under its control in Iraq and Syria after it swept through much of the Sunni Arab heartland north of Baghdad in June and then stormed minority Christian and Yazidi Kurdish areas.
"The massacres and abductions being carried out by the Islamic State provide harrowing new evidence that a wave of ethnic cleansing against minorities is sweeping across northern Iraq," said its senior crisis response adviser Donatella Rovera.
The UN Human Rights Council unanimously agreed to send an emergency mission to Iraq to investigate IS atrocities, after a senior UN official said the jihadist group had carried out "acts of inhumanity on an unimaginable scale".
Such strikes were used in the area during the Amerli operation -- the first time Washington has expanded its more than three-week air campaign against IS outside the north.
Desperate residents rushed to receive aid deliveries after Iraqi forces moved in to the town, scrambling to grab food and bottles of water from flatbed trucks.
A day after seizing Amerli, troops and Shiite militiamen on Monday retook Sulaiman Bek and Yankaja, two towns to its north that had been important militant strongholds.