IRBIL, Iraq — A coordinated attack on a restaurant and a security checkpoint in southern Iraq killed more than 80 people Thursday, police and health officials said, in a rare spasm of violence targeting a route used by Shiite pilgrims to visit their holiest shrines.
Gunmen wearing military uniforms stormed into a restaurant in Nasiriyah, about 200 miles south of Baghdad, around lunchtime and opened fire, the head of the provincial health department said. Patrons in the eatery included Iranian and Iraqi pilgrims traveling north toward the Shiite shrines in Karbala and Najaf.
Moments later, a car driven by a suicide bomber exploded at a police checkpoint near the restaurant, which sits along Highway 1, the road that connects Baghdad with Dhi Qar province, where the attack took place.
An additional 93 people were injured in the double attack, for which the Islamic State later claimed responsibility in a statement released online by its propaganda arm. The terrorist group has been steadily losing territory, most recently Mosul, its largest stronghold, and the smaller city of Tal Afar, but it has shown an ability to launch insurgent-style raids in areas it once held.
Iraqi officials have voiced fears that the group would step up its attacks on civilians as its grip on territory weakens.
Because the south is home to Iraq's most revered Shiite shrines, it is among the best-secured areas of the country and has rarely been the target of large-scale attacks. At the same time, though, many security forces assigned to the south have been drawn into battles against the Islamic State in the north and west, leaving some holes that terrorists have exploited.
Jassim al-Khalidi, the director of the Dhi Qar Health Department, said that 83 people were killed Thursday, most of them inside the restaurant, Fadak, a popular pit stop for pilgrims.
"This restaurant is well-known for being crowded every day because anyone who goes to Najaf and Karbala from the south stops there for lunch," he said in a telephone interview.
Khalidi said witnesses told him the gunmen came in three cars and began spraying the building with bullets from automatic weapons. The gunmen escaped, he said.
Videos posted on social media showed people frantically searching a hospital ward for their relatives.
One man spoke to the camera, saying he had dropped off his family at the restaurant, then was trying to fix something in his car when the shooting erupted. He said he saw the gunmen flee in black cars.
"I went back to the restaurant and found my entire family dead," he said.
U.S. officials said the Islamic State has been severely degraded since it lost 90 percent of the territory it seized in a 2014 blitz across Iraq. The cities and towns it once held contained factories for making car bombs and improvised explosive devices, and the loss of those facilities has reduced the group's use of explosives in its attacks on security forces and civilians.
Attacks involving mainly automatic weapons remain a major challenge, however. Gunmen have been able to breach security lines in cities reclaimed by Iraqi forces, such as Tikrit and Fallujah, often by wearing military uniforms and taking advantage of lax protocols at checkpoints.
In Mosul, residents have complained that some of the militants who patrolled their neighborhoods have reappeared unarmed and are quietly living among them. Although Iraq has detained and is in the process of prosecuting many people suspected of joining the Islamic State, corruption in the police and judiciary has allowed some to avoid arrest.
Some analysts say losing territory has not significantly affected the Islamic State's ability to wage terror on a smaller but still deadly scale.
The group is moving into a new, insurgent phase, said Michael Knights, a military analyst and Persian Gulf expert at the Washington Institute for Near East Policy, a nonpartisan think tank.
"ISIS is not a movement in disarray," he said, using an acronym for the group. "It has undertaken a smooth transition into insurgency, and doesn't seem greatly disrupted by the loss of terrain."