Bombs have exploded outside four churches across Baghdad, the Iraqi capital, killing at least four people and wounding 28 others, police have said.
A car bomb placed outside a church on Palestine Street in the east of the city on Sunday killed four people and injured 21 others.
Three bombs placed in cardboard boxes went off earlier near the gates of churches in the Ghadir and Karrada districts of central and eastern Baghdad.
Christians, believed to number around 750,000, have been sporadically targeted for attacks, particularly in Baghdad and the northern city of Mosul, leading many of them to flee abroad.
In the northern city of Kirkuk on Sunday, armed men assassinated Aziz Rizqo Nisan, the head of the provincial audit department - a Christian in a city divided along ethnic and sectarian lines.
Although violence has fallen significantly from a peak following the US-led invasion in 2003, there has been an increase in attacks as US combat troops have pulled out of the centre of towns and centres.
Two explosions outside a billiard hall in Baghdad on Saturday killed at least one person and wounded at least 20 others and a roadside bomb in the Saydiya district killed a junior cabinet official.
Despite the violence, a senior US military official said on Sunday that there had been calls for help with urban combat since the withdrawal on June 30.
"Here's what has not happened: there have been no requests for combat forces to return back into the city, any city," said Lieutenant-General Charles Jacoby Jr, the head of day-to-day operations in Iraq.
"There are established protocols for how [Iraqi forces] might ask for that, but we have not been asked for combat forces."
Jacoby acknowledged that there had been an increase in violence in recent days, but said that it had been expected, particularly in the Nineveh, Kirkuk and Diyala provinces.
"The networks were waiting for this time period and I think they're going to punch themselves out," he said.
General Babaker B. Shawkat Zebari, the Iraqi army chief of staff, said that armed groups targeting the government had been reduced to just a few cells, but they could continue attacks for "a year, or two or three".
He said that the Iraqi military would get help from American forces if needed, but would also rely on assistance from its own citizens.
"To face terrorism, the Iraqi army does not need tanks or armoured vehicles, but needs intelligence, fast communication and people's support," he said.