BAGHDAD (AP) — An aid group says 4,000 more people have fled the Islamic State-held city of Fallujah in Iraq after government forces retook a key road to the IS stronghold over the weekend.

The Norwegian Refugee Council, which works with refugees and internally displaced Iraqis, said on Monday that this brings the total number of residents who have fled Fallujah since the Iraqi offensive to retake the city started in late May to 27,580.

Aid groups estimate that 50,000 civilians still remain trapped inside Fallujah, which has been under IS control for over two years — the last major city in western Iraq still held by the extremist group.

NRC says some refugees reported that IS militants are demanding payments of 150,000 Iraqi Dinars, around $130, per person to let them leave.