BAGHDAD -- The black-masked soldier stood at the army checkpoint examining the identification cards of each passenger, denying entry to anyone who did not live in the Sunni district of Ameriya. One resident later said entering his neighborhood now felt like crossing the border into a different country.
"This neighborhood is full of bad people," said the soldier at the checkpoint as police officers rounded up people suspected of being terrorists in Ameriya, an operation that locals said targeted them only for being Sunni.
Across the country, the sectarianism that almost tore Iraq apart after the U.S.-led invasion in 2003 is surging back. The carnage has grown so bloody, with the highest death toll in five years, that truck drivers insist on working in pairs -- one Sunni, one Shiite -- because they fear being attacked for their sect.
Adel Ibrahim, a 41-year-old engineer, guessed wrong. On Aug. 6, to prepare for the evening iftar, the meal to break the day's Ramadan fast, Mr. Ibrahim went to a butcher shop in the central Karrada neighborhood to pick up meat for kebabs. Outside the shop, a Kia minivan exploded, killing Mr. Ibrahim and five others.
The drastic surge in violence -- mainly car bombs planted by al-Qaida's Iraq affiliate against the Shiite majority, and the security sweeps in majority-Sunni neighborhoods that follow -- has lent a new sense of Balkanization to this city. Security forces have increasingly restricted the movements of Iraqis in and out of Sunni areas, relying on the neighborhoods listed on residence cards as an indicator of a sect. Sunnis also fear reprisals from reconstituted Shiite militias, groups once responsible for some of the worst of the sectarian carnage that gripped Iraq just a few years ago.
The targets of the attacks are not usually government ministries or luxury hotels, places many ordinary Iraqis can safely avoid. They are the markets and cafes, mostly in Shiite areas, that dominate neighborhood routines. During morning commutes, some Iraqis are taking circuitous routes to work to avoid central streets where bombs have struck. The sight of a Kia minivan, a vehicle of choice for bombers, caught in traffic causes fear. Neighborhood soccer teams are canceling matches because those, too, have become targets.
After Mr. Ibrahim was killed, the next wave of attacks came four days later, on Saturday evening, as Iraqis were celebrating the end-of-Ramadan festivities known as Eid al-Fitr. A young bride-to-be, in her white wedding dress, sat in a hair salon when a parked car just outside blew up. The woman survived with only a small injury to her hand.
Across town that evening, a cigarette vendor named Jalal Hussain was wounded in another explosion. The next morning his stall was back in business. "It's a struggle for existence," he said, as he sold a customer a pack of Marlboros. "I have to feed my family. I have to open again, as long as I am alive. I have witnessed many other explosions, but this one was the closest. We have to keep on surviving. If you are lucky, you will survive another day."
Often, the fear briefly abates after a day of bombings. Surely, the thinking goes, big attacks will not come on back-to-back days.
"Customers are already calling to see if we opened or not," Mr. Haneen said on the morning after the explosion near his salon. "Today, I know there will be no explosions, as yesterday there were many. Maybe in the next two or three days we will witness another wave of bombings, but not today."
For Iraqis, the violence feels permanent, their country's perpetual decline, inevitable.