Angry relatives of missing Iraqi soldiers stormed the parliament building in Baghdad on Tuesday, attacked MPs and staged a sit-in for several hours in its main chamber, an official said.
They demanded information on the fate of relatives who surrendered to jihadists in June and also called for commanders to be held accountable, said the official, who was present in parliament.
The hundreds of demonstrators assaulted some MPs as well parliamentary staff, and smashed chairs in the cafeteria, he added.
Parliament had convened to discuss the issue on Tuesday, but the building was stormed before the start of the session.
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The protesters later left the building and parliament speaker Salim al-Juburi met with their representatives at his home, the official said.
An emergency session of parliament, with relatives in attendance, will be held on Wednesday, Juburi's office said in a statement.
Around 1,700 soldiers surrendered to the jihadist Islamic State (IS) group in June as its fighters seized second city Mosul and swept south towards Baghdad.
IS subsequently released photographs of dozens of men in civilian clothes apparently being executed by firing squad in a desert area, and said that it had killed hundreds in total.
Security forces were swept aside by the initial IS-led onslaught, but have since retaken areas northeast of Baghdad with the backing of Shiite militiamen and Kurdish fighters.