With new waves of civilians fleeing violence in Anbar there are now more internally displaced Iraqis, nearly three million, than there were at the height of the bloody sectarian fighting that followed the American invasion, when millions of Iraqis were able to flee to Syria. That door is closed because of that country’s own civil war. And now doors in Iraq are closing, too, worsening sectarian tensions as the Shiite authorities restrict where fleeing Sunnis can seek safe haven.

“We are all Iraqis,” said Marwan Abdul, a doctor’s assistant standing in frustration outside his mobile clinic here. “This wouldn’t happen in any other country.”

The violence unleashed by the Sunni militants of the Islamic State, also known as ISIS or ISIL, has hit Sunnis disproportionately. Nearly 85 percent of the Iraqis on the run are Sunnis, and they often find themselves seeking safety in Shiite-dominated areas, including Baghdad, where, as at the bridge here, they are frequently treated as security threats rather than suffering fellow citizens.