Shia militias have begun gathering close to the Iraqi city of Ramadi, which was captured by the Islamic State on Sunday.

The Iraqi government has requested the assistance of the troops – who are backed by Iran – in taking the key town following the routing of the Iraqi military forces, many of whom fled, the BBC reports.

The United Nations estimates that 25,000 people have fled the city, which is roughly 70 miles west of Baghdad.

The White House has described the loss of Ramadi as a 'setback.'