The curfew in Baghdad largely kept a lid on retaliatory attacks in the capital, but a number of Sunni Arab mosques were torched or blown up elsewhere in the country.
While cars and people returned to Baghdad's usually hectic streets after the curfew was lifted at 5am (01:00 GMT), residents said the capital was quieter than normal as some were still fearful of revenge attacks.
Bomb explodes in Kirkuk
The Kirkuk car bomb exploded near the office of a Kurdish party. Two security guards were among the dead, police and medical officials said.
Four more people, including two security guards, were wounded in the attack near the office of Patriotic Union of Kurdistan (PUK), the party of Jalal Talabani, the Iraqi president.
Police Captain Sharzad Mahmud said: "The bombers left an explosives-laden car on the road near the office in east Kirkuk's al-Askari neighbourhood and fled.
"The PUK security guards went to check the parked car when it suddenly exploded, killing the two guards and wounding four more, including two guards."