BAGHDAD (REUTERS) - More than 100 relatives of Iraqi soldiers abducted by Islamic State fighters broke into parliament armed with sticks, metal bars and stones on Tuesday, demanding news of their loved ones, witnesses said.

The crowd, mostly from Iraq's Shi'ite majority, smashed some equipment, assaulted at least two staff members they mistook for lawmakers and were refusing to leave the building, said officials inside.

"They were ready to bulldoze anyone standing in front of them ... They were saying 'Our sons are buried in the dust. We don't even know their names, and you are sitting here in comfort under the air conditioning'," a parliament employee said.

"A special force unit came with batons to remove them from the parliament ... I can hear screaming, shouting and name calling," the employee added.

Islamic State (ISIS) militants captured the soldiers in June at the start of its lightening advance through northern and central Iraq, where it declared an Islamic caliphate and threatened to march on Baghdad.

The soldiers walked out of their base in Tikrit, north of the capital, believing a truce had been brokered. Instead, ISIS took them and later reported it had killed 1,700 soldiers, posting pictures of corpses online.

There have been no independent reports on how many died. Locals in Tikrit said in June they believed the number was in the hundreds.

The relatives had been scheduled to address parliament about the fate of their loved ones. But they started to violently protest outside the building and then forced their way inside past several checkpoints, according to parliament employees.

"They broke into parliament. They roughed up some guards and officials. They broke the equipment (inside the assembly hall),"said another witness.

Some lawmakers fled, leaving briefcases and jackets behind, said one civil servant.