Forces fighting against the Islamic State have launched an offensive to retake the Iraqi city of Fallujah.

NPR's Alison Meuse reports that international aid groups have seen hundreds of civilians fleeing, but they represent only a fraction of those still trapped in the city.

Alison filed this report for our Newscast unit:

"Lieutenant General Abdel Wahab al-Saadi—who heads Fallujah operations—tells NPR by phone his forces are now on the southern edge of the city. The drive to enter Fallujah began at dawn, with air support from the U.S.-led coalition. In northern Iraq, U.S.-backed Kurdish forces are pushing to get closer to Mosul."Mosul and Fallujah are the last bastions of the Islamic State in Iraq."The Norwegian Refugee Council meanwhile warns tens of thousands of civilians remain trapped in Fallujah. Some 3,000 have managed to escape since the offensive began. But the council says it may not have enough drinking water for all of those displaced."

As the New York Times' Tim Arango explained on Morning Edition, Fallujah has been fought over for more than a decade. The current siege is being driven by militias, Arango said, who have started by clearing the agricultural outskirts of the city. This has been underway since December.

The siege, Arango said, has increased worries about the humanitarian situation inside the city.

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