Ban Ki-moon, the United Nations secretary general, released a statement condemning “in the strongest terms the systematic persecution of minority populations in Iraq” and particularly the threat against Christians.

And Prime Minister Nuri Kamal al-Maliki, who is struggling to remain in power as Iraq’s political factions negotiate to form a new government, said Sunday, “The atrocities perpetrated by ISIS against our Iraqi citizens, the Christians in Nineveh Province and the attacks on the churches and houses of worship in the areas that fall under their control, reveal without any doubt the terrorist and criminal nature of this extremist group that poses a dangerous threat to the humanity and the heritage and legacy that has been preserved over centuries.”

He called on the “whole world to tighten the siege on those terrorists and stand as one force to confront them.” That was perhaps a reference to the influx of foreign fighters into Iraq, many of whom have also fought in Syria’s civil war. On Sunday, ISIS issued a statement claiming responsibility for two suicide attacks in Baghdad on Saturday, and said that one had been carried out by a German citizen, and the other by a Syrian.

The gathering on Sunday at St. George Chaldean Church, built in 1964 and situated in a Shiite Muslim neighborhood, was as much about Iraqi solidarity as it was a gesture of condemnation for the persecution of Christians. In many ways Iraq’s struggle today is the same as it has been since the country was founded nearly a century ago, at the end of World War I: how to establish a national identity larger than a particular faith or ethnicity.

In the pews Muslims and Christians alike held signs that read, “I’m Iraqi. I’m Christian.” Muhammad Aga, who organized the event over Facebook, spoke, and listed Iraq’s many narrower identities: Christians, Arabs, Kurds, Shabaks, Turkmen, Yazidis, Sunnis and Shiites. “All of those people who carry Iraqi identity,” he said.

The church’s patriarch, Louis Raphael Sako, said, “I carry every Iraqi in my heart.”

After the service, two men, cousins in their 60s, stood in the church courtyard. They grew up in Mosul, and moved to Baghdad as teenagers. They have witnessed much of Iraq’s traumatic history of coups, revolutions, wars and sectarian cleansing, and have stayed the whole time.

“You have to be angry,” said Faiz Faraj, 65, a retired teacher. “You must cry.”

But, he said, “Iraqis have suffered for a long time, but this will pass.”

His 9-year-old granddaughter, Lana Fanar, recited at the service a poem written by a well-known Iraqi poet in 2006, as Iraq was in the grip of sectarian killings. Its words could be spoken of any of Iraq’s previous traumas, or today:

“I cry for my country. I cry for Baghdad. I cry for the history and the glory days. I cry for the artists, for the water, for the trees. I cry for my religion. I cry for my beliefs.”