“Our celebrations will not be open and will be restricted to going to the church in the morning,” said Naeil Victor, a 58-year-old teacher in the southern city of Basra. “My children are upset because they have been waiting for this Christmas for a year now, but my wife and my father understand what is going on around them.”

Image Mass at St. Joseph Chaldean Church on Sunday. Christians are being asked for identification at Baghdad churches this week. Credit... Eros Hoagland for The New York Times

Some churches have dozens of soldiers and police officers positioned around them after the government placed security personnel on high alert because they received the names of churches that extremist groups said would be bombed on Christmas Day. Other churches have received individual threats.

In Mosul, during the past month, three churches have been bombed, killing a baby and wounding 40 other people. Last week, a Christian man in Mosul was shot dead as he walked down a street.

At least one church there has decided to relocate its Christmas Mass from Mosul to a small town about 30 miles north because parishioners say they feel it will be safer for them.

“We have moved the rituals for Christmas to the town of Qereqush, fearing that the Christians might be harmed in this insecure and unsafe city,” said the Rev. Behnam Asaad of Qahira Church. “We have distributed cards and fliers to the Christian families of this church informing them about the time and place where we will have the celebration, but we fear that assassinations might take place even after Christmas.”

Mr. Asaad said that he had received letters as recently as Monday from armed groups threatening to blow up churches and monasteries, including his own, if they celebrated Christmas.

Many Christians however, said they were unconcerned about the possibility of being attacked, saying they were suffering no more than other Iraqis.