AMERLI - Iraqi forces made more progress Tuesday in their fightback against militants but in Baghdad anger boiled over as hundreds stormed parliament over the fate of missing soldiers who surrendered in June.After breaking a months-long militants siege by Islamic State fighters of the Shiite Turkmen town of Amerli, 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 militants 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.That collapse left some 1,700 soldiers in jihadist hands, with many believed to have been executed. Demanding to know their fates, angry relatives stormed the parliament building in Baghdad, attacked MPs and began a sit-in in its main chamber, an official said.Anti-riot police were trying to force out the hundreds of protesters, who were also calling for some officers to be held accountable, said the official, who was present at parliament. 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.IS has carried out beheadings, crucifixions and public stonings and Amnesty International on Tuesday accused the militants of ‘war crimes, including mass summary killings and abductions’ in areas under its control. ‘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.’ Concern over the scale of the humanitarian crisis helped prompt Washington to begin carrying out limited air strikes in support of Iraqi forces, Shiite militia and Kurdish troops battling the militants. 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. Army Staff Lieutenant General Abdulamir al-Zaidi said they had continued the advance on Tuesday, regaining control of a stretch of the main highway to the north which had been closed by the militants for almost three months. A senior militia commander said it would be several days before the road reopened as sappers needed to clear it of mines and booby-traps planted by the retreating militants.The United States said it launched four air strikes in the Amerli area, meaning that it effectively supported operations involving militia forces that previously fought against US troops in Iraq. The government’s reliance on Shiite militiamen in this and other operations risks entrenching groups which themselves have a history of brutal sectarian killings. David Petraeus, a former commander-in-chief of US-led forces in Iraq, has warned against America becoming an ‘air force for Shiite militias’.But worries over the rise of IS seem to be outweighing other concerns, with Western leaders warning the group poses a security risk far outside the areas under its control. Australian Prime Minister Tony Abbott on Tuesday said that ‘extreme force’ was justified against IS militants, describing them as worse than Nazis or Communists. ‘As soon as they’ve done something gruesome and ghastly and unspeakable, they’re advertising it on the Internet for all to see which makes them, in my mind, nothing but a death cult,’ Abbott said. Hundreds of Western nationals are believed to have travelled to Iraq and Syria to fight alongside IS, prompting fears over their return. British Prime Minister David Cameron on Monday announced tougher measures against suspected returning militants, including giving border police powers to seize passports. IS and its allies control a large swathe of northeastern Syria as well as territory in Iraq, and its rule has been marked by repeated atrocities, some of them videotaped and posted on the Internet. Washington has said operations in Syria will be needed to defeat IS, but has so far ruled out any cooperation with the regime in Damascus.