Followers of the Shia group of Kata'ib Sayyid Al-Shuhada - the Battalion of the Sayyid's Martyrs, left Iraq's southern city of Basra on Sunday, heading to Baghdad to join the Iraqi army and fight against Sunni insurgents - led by Isis (the Islamic State of Iraq and Syria), who seized a number of Iraqi cities in recent days. An estimated 500,000 Iraqis have already fled Mosul, home to some two million people